An introduction to the water structure problem

Although the macroscopic properties of water have been heavily studied, there are things we don’t understand about this ubiquitous substance. In this post, I will provide an introduction to the problem of describing water’s structure. At first glance, the idea of a liquid having structure seems preposterous. Indeed, liquids cannot maintain a structural arrangement of atoms like solids can. Instead, the atoms/molecules tumble past each other in constant state of motion. This allows for the defining property of the liquid state – the ability to fill a container.  

However, one can talk about an average local structure in the following sense – if you were to sit on a water molecule’s oxygen atom and observe where other molecules are around you, over time you would notice that the nearest neighboring molecules tend to be in certain places. This average structure can be quantified in a radial distribution function, which shows the likelihood of observing other atoms at different distances r from a central atom:

Example oxygen-oxygen radial distribution function, showing experimental data from x-ray diffraction and calculated from a simulation with the TTM3F model.

Example oxygen-oxygen radial distribution function, showing experimental data from x-ray diffraction and calculated from a simulation with the TTM3F model.

If the positions of atoms are completely random, then the RDF equals to 1. Where it is greater than 1, that indicates an average excess of molecules at that distance, and where it is less than 1 indicates a deficit. Note that by this measure, structure does not extend that far out – only 10 Angstroms (1 nanometer) at most. Looking at RDFs is by no means the end of the story, as we will see. For one thing, rdfs are spherically averaged. To get a more complete picture one can also make 3D plots. For instance, at the distance of r = 2.8 Angstroms:

3d_rdf

3D plot from a ab-initio density functional theory simulation. The blue lobes show regions where there is a high probability of finding other water molcules. The distance corresponds to the hydrogen bond distance. The tetrahedral symmetry that comes from hydrogen bonding is very apparent.

struct_diffs_hdl_ldl

Figure from here.

This plot was obtained from quantum-mechanical simulations performed a previous grad student in our group, Jue Wang. In addition to doing the spherical averaging, RDFs do not tell us if the local structure varies through the liquid. For instance, there might be regions where each molecule has more hydrogen bonds on average, (more “ice-like”) which would cause the water in that region to have a lower density. Correspondingly, there might be regions where molecules have less hydrogen bonds, and more ‘interstitial’ molecules, which would cause a higher density.  The idea that water may be inhomogeneous goes back to 1892, when W.K. Roentgen proposed that water contains a mixture of two structural motifs – “ice like” and “liquid like”. The idea helps explain many of the anomolies of water, such as the fact that water has a density maximum at 4 C. If you cool water below 4 C, it expands, which is highly anomalous. This could be explained though if the low density regions start to dominate below 4C.

what does the phase diagram of deeply supercooled water look like?
The debate about water structure dovetails with a debate about the low-temperature behaviour of water.

phase_diagram

The regime were water can be supercooled and the different forms of amporphouse (glassy) ice. Figure from here.

Water can be easily supercooled down to -20 C. However around -45 C one runs into a hard limit, and water always freezes. There is much interest, however, in how about how water would behave if it could be supercooled even lower. This hypothetical part of the diagram is called the ‘no-mans land’.

Interestingly, it is possible to create amorphous ice (sometimes also called glassy water). One way to do this is to cool water at an extremely rapid rate. If the cooling is done quickly enough, the water molecules don’t have time to freeze into ice, and they are trapped in a ‘glass’ which is technically a supercooled liquid state, but so cold that it behaves like a solid. Another way of making amorphous ice is by putting normal ice under high pressure.

At different pressures amorphous ice exists in two forms, low density (LDA) and high density (HDA), with a sharp phase transition between them. The video above shows what happens when you remove the pressure on HDA — it quickly converts to LDA.

Now, you might think you could make supercooled water in the ‘no-mans land’ part of the phase diagram by heating up amorphous ice. Unfortunately, if you do this it turns into regular ice, because at higher temperatures the water molecules can move around more and adopt their preferred form.

There is a great debate in the scientific community about what the “phase” diagram is in the ‘no-mans land’. The term “phase” here is technically incorrect, because supercooled water is not a true thermodynamic phase, rather it is a metastable state. In any case, in a seminal 1992 Nature paper it was proposed that at some point in the no-mans land there is a second order critical point.

To understand what a 2nd order critical point is and why this would be important for room temperature water, consider the phase diagram of water shown in Chemistry 101 and Physics 101 textbooks:
Phase-diag2.svg
Now let’s flip it and rotate it that pressure is on the x-axis and temperature is on the y-axis, so we can compare to our previous diagram:
Phase-diag2.svg_rotated
The blue line shows the transition between liquid and gas. The red point at the top of this line is an example of a 2nd order critical point. Above this point, there is no sharp distinction between liquid and gas. Water above the critical point is called ‘supercritical’. In super-critical water there are very large density fluctuations (inhomogeneities!).

Similarly, if a 2nd order critical point exists in the no-mans land between LDA and HDA, then liquid water should contain density fluctuations between HDL (high density liquid) and LDL (low density liquid).

Another diagram has been purposed though, called the ‘singularity free‘ version, and there is great debate about how to prove which picture is correct currently raging in the scientific community, which I don’t have space to go into here. Many scientists like the concept of a critical point in the no-mans land, though, because it helps explain many strange anomalies observed in studies of supercooled water. Many of the properties of supercooled water, such as its compressibility, anomalously start to increase when water is supercooled and follow a trajectory that would lead to a singularity if a low enough temperature could be reached.

is room temperature water homogeneous or inhomogeneous?
During the 80’s and 90’s there was also intense debate between experimentalists about how many H-bonds water molecules have.  By the early 2000’s, most scientists had reached a consensus that the average number was around 3.5, that the H-bond network filled all of space and was mostly tetrahedral, and that density inhomogeneities were small at room temperature.  A 2004 x-ray scattering experimentalists challenged this view by proposing that water contains many molecules with only 2 hydrogen bonds which are connected in long chains. This was debated for some time and is now largely believed to be il-founded.

A greater challenge, still being discussed today, came with the publication of “The inhomogeneous structure of water at ambient conditions” by Huang, Nilsson, et al. in 2009. Their argument largely rests on their interpretation of small angle X-ray scattering (SAXS) data, which probes changes at long wavelengths, on the order of nanometers.  They find that at long wavelengths there is an unexpected increase in the scattering of x-rays. The authors tried to reproduce this result by doing a molecular dynamics simulation and  were unable to. Their implication was that molecular dynamics simulations can not be trusted to settle the debate about the structure of water. However, such things from simulation is very computationally expensive. Later simulations by Sedlmeier, Horinek, and Netz that used a better calculation method did recover the excess response.

What molecular dynamics simulations show
Molecular dynamics simulations with the most optimized models (which have names like TIP4P/2005f) do show the co-existence of clearly defined HDL-like and LDL-like domains at very low temperature. For instance, Overduin and Patey simulated at the chilly temperature of 175 K, in a long box rectangular box with dimensions 12nm x 3 x 3nm:

The top panel shows where molecules identified as “ice-like” are, in red. The bottom panel shows differences in density, with regions with lower density than average (ice-like) also shown in red. The x-axis represents time. Notice that there is switching between the two types of local structure with a timescale on the order of microseconds (1000 nanoseconds). Such switching back and forth was observed in other simulation work that simulated a smaller box of supercooled water for several microseconds.

While this is neat, simulations do not show any such heterogeneity in room temperature water.(ref) However, one can look at the distribution of the parameter Q4, which measures tetrahedrality around each molecule. If the nearest neighbors were like they are in ice (nearly perfectly tetrahedral) then Q4=1. If they are random, Q4=0.  There is a distribution of Q4 found in room temperature water with a peak around .8.  Sedlmeier, el al. found that correlations in Q4 do not extend beyond 6 Angstroms, or the 2nd H-bonding shell.

If not nanometer scale heterogeneity, then could cause the excess x-ray scattering Huang et al observed?  In a 2010 article in PNAS, it was suggested that normal stochastic density fluctuations can also explore the data. In my view neither this picture or the idealized picture of HDL/LDL domains are fully satisfying explanations. Both effects may be at play.

The current view that is most consistent with the experimental data is that room temperature water contains a hydrogen bond network that extends through all of space which is severely distorted in places, and may contain local inhomogeneites. Overall the network has a largely tetrahedral character with a most molecules having 3 or 4 hydrogen bonds (avg 3.5-3.9). Our Nature Communications paper shows how optical phonons propagate through this network. This type of overall homogeneity does not preclude the existence what we have called ‘polar nanoregions‘. This is because polar ordering has more to do with the relative orientations of the hydrogen atoms while structural ordering has more to do with the position of oxygen atoms.

The extent and nature of inhomogeneites in room temperature water remains controversial. A Dec. 2015 Nature Communications review by Nilsson & Pettersson in Nature Communications defends the validity of the two-state approach to understanding water several lines of experimental evidence, but controversially invokes a picture of HDL/LDL domains even at room temperature.

The accuracy of MD simulations can always be called into question, but no present day experiment can resolve the controversy about the structure of room temperature water, simply because there is no microscope that allows us to see structure as it extends over nanometers. Our recent work, discussed in my previous post, opens a new window into probing the local structure of water through the analysis of dielectric spectra, which we believe can bring more clarity to how water’s local structure changes with temperature.

13 Comments

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13 Responses to An introduction to the water structure problem

  1. James McGinn

    This is an excellent blog post. I really appreciate the clarity of the thinking being presented here. I will be leaving a larger comment, putting a spin on it that further makes the case for my model, but I just wanted to pay a compliment for such an excellent post.
    Regards,
    James McGinn

  2. James McGinn

    Although the macroscopic properties of water have been heavily studied . . . At first glance, the idea of a liquid having structure seems preposterous.
    I love the clarity of your writing and how you have framed the issue. Good start!
    . . . if you were to sit on a water molecule’s oxygen atom and observe where other molecules are around you, . . .
    This is very clearly explained. Only if there is a pattern would we be able to predict where another oxygen atom is located.
    This average structure . . .
    I have a problem referring to this as, “structure.” I think it is “arrangement”, not “structure”. I understand your premise. You are asserting that structure does not necessarily imply or require that the molecules are actually touching. There is more to my objection than just semantics. And I do realize the issue you are trying to resolve. And I realize that this issue is bolstered with data–allegedly valid data. So I am sympathetic to why you would use the word ‘structure’. I will explain why such special pleadings are not necessary with my model.
    This plot was obtained from quantum-mechanical simulations performed by a previous grad student in our group, Jue Wang.
    Excellent. Your explanation is crystal clear. I can see that this involves looking at it from three different angles to construct a 3 dimensional model in your audience’s mind. Well done! Nevertheless your model is mistaken. I can explain why.
    In addition to doing the spherical averaging, RDFs do not tell us if the local structure varies through the liquid. For instance, there might be regions where each molecule has more hydrogen bonds on average,
    I understand. It is an idealized model. These are statistical distributions. And you have done a good job of describing what your data indicates ACCORDING TO THE ASSUMPTIONS of your model. In other words, starting from your ab initro (first principles) of your approah this is what you model indicates. But what if your ab initro is wrong? What if we introduced different ab initro principles? What would the model look like if, instead, you started with ab initro assumptions based on the thinking in my paper? Might such a model reconcile all (or more) of the anomalies of H2O than your model? (I mean, let’s be honest, the standard model has existed for a long time and the anomalies remain mostly unresolved.) I will present a larger argument to this effect toward the end of this message. But there is a larger, more all-encompassing issue we have to deal with, the difference between how you and I envision ice:
    . . . there might be regions where each molecule has more hydrogen bonds on average, (more “ice-like”) which would cause the water in that region to have a lower density.
    The idea that water may be inhomogeneous goes back to 1892, when W.K. Roentgen proposed that water contains a mixture of two structural motifs – “ice like” and “liquid like”. The idea helps explain many of the anomalies of water,
    Here is the largest issue that blocks you from comprehending my model. For you ice involves an idealized notion of a lattice–more hydrogen bonds. For me ice involves asymmetric bonds, a consequence of bond breaking (which activates dormant polarity–see my hypothesis for details). This is also true for my conceptualization of surface tension, which is a form of ice in my opinion. (Bear with me on this one. I guarantee the argument will make sense in the long run. You need to temporarily suspend disbelief.)
    You and all the other “insiders” cannot remotely imagine that this idealized lattice structure notion of ice could be wrong. But if I was to put you on the spot and ask you to supply the empirical evidence that substantiates the validity of this notion you couldn’t comply. If I then pushed further and asked you why you believe something the validity of which you cannot substantiate you might, at best, shrug your shoulders and say, “Well, everybody believes it.” And except for me that is true. But that is exactly the reason you should look at it with more skepticism. Whenever you find something in a scientific discipline, any discipline, and everybody believes it and the only reason is because everybody believes it, you know you have found something that is, very likely, false.
    The tendency for people to be unable to break away from the psychological attraction of an idealized notion is a long-continuing issue in science. They often are blissfully unaware that the idealized notion is just a conjecture and not a truth and they are seduced into ignoring evidence that contradicts it. And this can go on for generation after generation, spanning hundreds of years. The classic example is that of the Ptolemaic theory of celestial motion. It contained idealized notion of planets moving in perfect circles. Even though Galileo showed that Ptolemaic theory was fundamentally flawed it took hundreds of years before Newton’s thinking showed that planets actually move in ellipses, not perfect circles, and only then was Ptolemaic theory abandoned.
    By the way, there is no shortage of evidence that actually disputes the idealized notion that ice is a tetrahedrally coordinated lattice. Although you will undoubtedly dismiss or minimize it because it doesn’t fit into your paradigm, here is quote from an abstract that I interpret as suggesting that the issue is not quite as clear as you and your insider cohorts would have the rest of us assume:
    http://scitation.aip.org/content/aip/journal/jcp/137/4/10.1063/1.4736853
    Investigation of the hydrogen bonding in ice Ih by first-principles density function methods
    P. Zhang1,2, L. Tian1, Z. P. Zhang1, G. Shao3 and J. C. Li1,a)
    “. . . reproducing the two experimental optic peaks do not need to invoke the two H-bonds as proposed in the previous model which led to considerable debates. The results of this work suggest that the observed optic peaks may be attributed to the coupling between the two bands of H-O stretching modes in H2O.”

    The first thing you have to realize about the idealized notion of a lattice structure for ice is that nobody has actually ever observed it. The notion began in the 1920s when Bernal (I think) created some models of H2O and began fitting them together to form idealized lattices. One thing about humans is that seeing is believing. When people saw these models and how neatly the pieces fit together they fell in love with them, and their ability to think rationally went out of the window. Thusly an honest conjecture that H2O molecules fit into a lattice for form ice became accepted as a dishonest “truth”.
    You might be wondering, why am I making such a big deal about ice. Here is the reason: it gets to the heart of your misconception about structure. You genuinely believe that tetrahedral coordination equals structure. (In fact, you believe it so deeply you are trying to insinuate [above] that if we call “arrangement” “structure” it solves the problem.) To you it is incomprehensible that anybody would assume otherwise. And you have done a very good job here of making that assumption explicit (which I appreciate). But you are wrong. In reality tetrahedral coordination neutralizes polarity. So tetrahedral coordination is associated with weak bonding. It is associated with the fluidity of liquid water, not ice (see my paper for details).
    Additionally, tetrahedral coordination is associated with HIGH density, not low density. And so, your confused belief that tetrahedral coordination equates to structure is exacerbated by the fact that you think the lattice explains the low density of structure (expansiveness of ice, for example). Being intrinsically less dense than symmetric bonding, asymmetric bonding explains the lower density of structure (ice). In other words, low density is asymmetric, not symmetric. And this underlies the expansiveness of ice. And asymmetry activates polarity, explaining the structural strength. Structural strength is not due to tetrahedral coordination, it is due to polarity being activated by asymmetry, the fundamentals of which are explicated in my paper.
    So, you guys are confused on a fundamental level. And your confusion stems from an idealized notion of ice being tetrahedral, when in actuality is is asymmetric. One piece of evidence that demonstrates that I am right and you are wrong is surface tension. A surface restricts completion of fully coordinated hydrogen bonds. It forces lower density, asymmetric bonds. This activates polarity. Activated polarity explains structural strength. But here is the thing. In order for this to work the hydrogen atom of an asymmetric bond MUST be touching the oxygen atom of the adjacent molecule to which is is forming the hydrogen bond. In other words, you can’t have structural strength unless you have molecules actually touching.
    It is at this point, Daniel, that I can imagine you wanting to scream into the computer screen as you read this. So let me do if for you:
    WAIT! WAIT! WAIT! JIM. ARE NOT PAYING ATTENTION? DID YOU NOT SEE OUR MODEL. OUR MODEL IS BASED ON EMPIRICAL DATA USING XRAY RAMAN. IT IS VERY CLEAR THAT THERE IS NOTHING IN THAT MODEL THAT INDICATES THAT THE H2O MOLECULES ARE ACTUALLY TOUCHING.
    I am paying attention. (And there is no reason to scream.) And I don’t dispute the data. I dispute your interpretation of the data. Specifically, I dispute the ab initro assumptions. In other words, you “insiders” have systematically misinterpreted the Xray raman data so you have built models that have nothing to do with reality. I suggest the following:
    Put aside your ab initro assumptions and instead assume the ab initro assumptions from my model.
    Put aside your idealized notions about ice and structure being tetrahedrally coordinated and open yourmind to the possibility that structure might actually have something to do with polarity being activated, as indicated in my model.
    Use the same data from that xray raman studies and construct a new model.
    As you know, the xray raman methodology does not directly measure the locations of the adjacent O or H atoms associated with H bonds. Instead they knock an electron out of the inner shell of the oxygen atom, allowing one from the outer shell to fall into the inner shell, and then they measure the infrared energy that is the result of that electron falling to a lower energy state on the oxygen atom. The resulting infrared energy signature allows them to make inferences about the locations of the adjacent O or H atoms.
    To make a long and complicated explanation short and to the point this is what it comes down to. In my model when proximity between the hydrogen atom and the oxygen atom increases the energy level of the electrons on the oxygen atom decrease and vice versa, the further they are the higher is the energy level. And this is because hydrogen bonding neutralizes polarity, neutralizing the energy level of the electrons, as explained in my hypothesis. Thus you have transposed the significance of your data. Specifically, you have misinterpreted the significance of the low energy levels indicated in the data. The data doesn’t indicate the hydrogen atoms are hovering at a distance. Your data indicates the hydrogen atoms are always very close to the oxygen. Higher energy levels don’t indicate closer, stronger symmetrically coordinated bonds. They indicate stronger asymmetric bonds in which one of the hydrogen atoms has been pulled away or they indicates symmetrically coordinated bonds in which there is increased (not decreased) distance between the hydrogen atoms and the oxygen atom. Lower energy levels don’t indicate weaker, structurally weak asymmetric bonds, they indicate weaker and very close tetrahedrally coordinated bonds.
    As I stated above, the evidence that demonstrates that I am right and you are wrong is surface tension. A surface restricts completion of fully coordinated hydrogen bonds. It forces lower density, asymmetric bonds. It activates polarity. Activated polarity explains structural strength. And surface tension is one of many H2O anomalies that my mody explains that your model cannot.
    Regards,
    Jim McGinn
    BREAKTHROUGH: Hydrogen Bonding as The Mechanism That Neutralizes H2O Polarity
    https://groups.google.com/d/msg/sci.physics/Cin1MQ4ZyFU/QmNEM9mnDgAJ

  3. James McGinn

    ” . . . there is no microscope that allows us to see structure as it extends over nanometers.

    “Our recent work, discussed in my previous post, opens a new window into probing the local structure of water . . . ”

    You missed the significance of your own work, in my opinion. Your work demonstrates that this in-liquid-water structure (low density anomalies) indicates molecules literally touching/attached to each other. I can’t imagine you do not at least suspect this. But you can’t bring yourself to admit/accept this because you know–rightly–that it conflicts with everything you’ve been taught. You are so determined to obediently comply with what everybody else thinks that it has even brought you to submit a plainly absurd explanations, the notion that if we just pretend ‘arrangement’ equates to ‘structure’ that we can pretend the current model makes sense.

    The current model fails because it was constructed by people that didn’t fully understand fundamental principles in chemistry, like electronegativity, symmetry, and the pivotal significance of the electron cloud, which is effected by proximity to positive hydrogen atoms in the same way regardless of whether the hydrogen atom is attached covalently or not.

    Your model (the standard model) is nonsense not because the data is bad, but because the ab initro assumptions are tacked on based not on factors that are generally true of other molecules but not of H2O. (In reality there is an inverse relationship between magnitude of the force of the charge and proximity of the hydrogen atom to the oxygen atom. This is a consequence of the fact that hydrogen atoms neutralize polarity.) And so, the correct way to interpret blue colored distributions in the model constructed by Jue Wang you would want to invert all of them relative to the molecule. Also, the molecules are generally much closer together (You’ve interpreted low and zero charges of your data as being at distance when in actuality it indicates closeness.)

    But the factor that overrides all of this isn’t so much a scientific factor as it is a human foible, the tendency of us humans to become religiously attached to idealized models, like this notion that ice involves a tetrahedrally coordinated lattice.

  4. James McGinn

    “This was debated for some time and is now largely believed to be il-founded.

    A greater challenge, still being discussed today, came with the publication of “The inhomogeneous structure of water at ambient conditions” by Huang, Nilsson, et al. in 2009.”

    The debate continues and will continue indefinitely as long as the paradigm assumes the following:
    symmetric bonding = low density = structural strength (ice)
    asymmetric bonding = high density = structural weakness (fluidity, low viscosity)

    The correct relationship is the following;
    symmetric bonding = high density = structural weakness (fluidity, low viscosity) = polarity neutralized
    asymmetric bonding = low density = structural strength (ice) = polarity activated (de-neutralized)

    Until you all get this relationship straight in your minds the data will continue to stir the water of the debate into indefinitely.

    • delton137

      I think the view is as you say – more distorted structures (allowing high density) have more asymmetry. I’ve never heard of there being a clear correspondance though.. and certainly not an expert on H-bonding.

      What I do know is that quantum simulations of liquid water show there is significant charge asymmetry in H-bonds. This is important, because it can explain the “pre-edge” seen in X-ray scattering. The cause of the “pre-edge” has been source of controversy. It was originally proposed to be associated with 1D long chains of molecules in the liquid.

      Thomas D. Kühne’s work on the subject has been highly publicized. They show the pre-edge can be explained by the charge asymmetry.
      http://www.nature.com/ncomms/journal/v4/n2/abs/ncomms2459.html
      I see he has another paper on the same the subject. (i haven’t read either)
      http://pubs.acs.org/doi/abs/10.1021/ja411161a

      I honestly do not really understand the details, (which get rather technical) only the high level overview. Incidentally, my adviser told me recently that her research from 2005 reached basically the same exact conclusion as Kuhne:
      http://arxiv.org/abs/cond-mat/0507319

      • James McGinn

        If your ab initio contains some kind of fundamental flaw (either inclusionary or disclusionary or both) then the model you build is going to be mistaken and you aren’t going to have any way of knowing. Collecting more data isn’t going to reveal the flaw but will instead give you a false sense of confirming the validity of the previous model.

        I’m continually amazed that so many who are involved in the study of water structure take H bonding for granted. When you fully comprehend how H2O polarity is variable and not constant and how H bonds are the mechanisms thereof it changes everything, including ab initio.

        I’m not exactly sure what the “pre-edge” issue is, but I suspect it is an artifact of the flaw or absence in your ab initio–also.

  5. James McGinn

    D.E.: “However, one can talk about an average local structure in the following sense – if you were to sit on a water molecule’s oxygen atom and observe where other molecules are around you, over time you would notice that the nearest neighboring molecules tend to be in certain places. This average structure can be quantified in a radial distribution function, which shows the likelihood of observing other atoms at different distances r from a central atom:”

    J. M.: Like much of current thought on water, which draws upon and is additive to some of the worst thinking in climate sciences and other related sciences that pander to public sentiment, what you are stating here, Daniel, is spiritualistic, not scientific. It’s regrettable that this kind of non-scientific thought has become so pervasive that no real, empirically driven, scientist has much of a chance of making progress.

    You are erroneously equating arrangement to structure. This is a plainly invalid argument. You are asserting spiritualism as an explanation. And then you are hiding your spiritualistic explanation in sciencey sounding rhetoric like, “This average structure can be quantified in a radial distribution function, which shows the likelihood of observing other atoms at different distances r from a central atom:”

    Structure can only involve molecules touching and forming a solid and. largely if not completely, an immovable connection. Reality doesn’t conform to semantics, no matter how cleverly we employ it.

    Obviously you are doing this because you are trying to not rock the boat of the current paradigm. However, the current paradigm is nonsense. The fact that all your teachers tell you it is true and the fact that there is a long tradition of people that don’t doubt it doesn’t make it true. Science involves facts, not beliefs, not tradition, not political correctness. 97% of the people in science are just along for the ride. Ignore them. They are irrelevant. They are believers. They are not scientists.

    • delton137

      I understand why you don’t like the word “structure” being used, but the definition of “average (local) structure” I give is rigorous.

      “97% of the people in science are just along for the ride.” – I’m not sure about that. Most scientists I know are very critical thinkers. Everyone scientist wants to discover flaws in previous work or develop new, more accurate theories and models. Doing so is tough though, because any theory about water has to reproduce all of the properties of water that have been unambiguously determined over decades of research.

      People come out with new ways of quantifying water structure & dynamics every year. Some are found to be useful for understanding water and some are not useful. In my previous paper we look at dipole-dipole coorelation functions, for instance. The framework of using RDFs is useful because RDFs can be easily measured from x-ray and neutron scattering experiments – that is why I discuss it here. Dipole-dipole correlation functions and other esoterica is hard get from experiment.

  6. James McGinn

    “I understand why you don’t like the word “structure” . . .”

    I think what I stated is very clear that my dispute is neither semantic nor aesthetic.

  7. James McGinn

    ” . . . any theory about water has to reproduce all of the properties of water that have been unambiguously determined over decades of research.”

    In your opinion is there anything ambiguous about the 70 plus anomalies that are associated with current theory?

  8. James McGinn

    “Doing so is tough though, because any theory about water has to reproduce all of the properties of water that have been unambiguously determined over decades of research.”

    The problem is that few have the ability to distinguish between what is unambiguously determined and what appears to he unambiguously determined. So progress comes to a standstill, as we see now in water sciences. You yourself substantiate this by the fact that you are defending a model that has failed to resolve upwards of 70 anomalies. You should be eager to discard such a dismal failure of a model, but you are not. If that is not the definition of a pathological science I don’t know what is.

    I want to present you with a challenge, Daniel, to see if you can think outside the box–to see if you have the intellectual fortitude to directly address new thinking. See if you can directly address what is stated here, without turning to your advisor:
    https://youtu.be/LwSyalcoRAk?t=11m33s

  9. James McGinn

    Science is confused about water because they are confused about polarity. They see polarity as a function of “polar’ bonds (a “polar” bond is a covalent bond that has an electronegativity difference). It’s not that simple. Many molecules have “polar” bonds but are not polar (they are not dipoles). A polar molecule is asymmetrical in addition to having electronegativity differences. And where it really gets confusing is when you consider that with water (and only with water) symmetry is variable–AND ACTUALLY VARIES AS A CONSEQUENCE OF HYDROGEN BONDING!

    In water polarity drops to zero when symmetry is achieved through coordinated tetrahedral bonds. The failure to comprehend this and its implications is the reason they are so perplexed by water and its many anomalies. For example, once you understand this it becomes immediately apparent why H2O has its high heat capacity. Strangely, the professionals have no ability to grasp the importance of symmetry to polarity. They write paper after paper and do video after video that demonstrates their ignorance of the intricacies of polarity and then they make lists of water’s anomalies, pretending they have explained something that they have not explained. The following paper tries to get beyond that same ground hog day, over and over again, glossing over, inability to grasp what is really happening at the molecular level that is so typical of the study of water:

    https://zenodo.org/record/37224

  10. James McGinn

    Ultimately the biggest issue preventing the resolution of the water structure problem is psychological, the tendency for humans to be aesthetically attracted to idealized notions. And, in this case, that manifests itself in this absurd notion that the structure of ice is the result of water molecules forming into a lattice. This notion was assumed back in the 1930’s and persists despite the fact it has never been verified. It is believed. And it is a huge obstacle because it gives researchers the false belief that they can ignore what is actually the best evidence we will ever have to untangle the water structure problem, that being the evidence associated with the transition between liquid water and solid ice.

    If researchers were forced to admit that the body of evidence associated with this transition was not yet properly explained they would be forced to conclude that there must be some mechanism that is activating polarity over this transition. (Because without this there is no way to reconcile why and how this transition is so discrete and why and how there is such a sharp distinction between the hardness of ice and the fluidity of liquid water.) And this would force them to recognize that, therefore, polarity must be turned off (neutralized) in liquid water. And this would force them to seek out the mechanism that achieves this polarity neutralization in liquid water–which I’ve already discovered: https://zenodo.org/record/37224

    As with much of what can be found in the literature of the structure of bulk water, the notion that water molecules can arrange themselves into a lattice is idealized, pseudo-scientific, phantasmagorical fiction. It is a science-based fairy tale. Only after researchers can psychologically bring themselves to admit that this notion is nonsense will there be any chance of making progress. Of course that means that no progress will be made until the people that lead the sheep in this intellectually dead discipline retire or die.

    James McGinn
    jimmcginn9 at gmail dot com

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