Presentation on theme: "40 years of quantum chemistry from polywater to the real stuff Ad van der Avoird Nijmegen, 25 April 2008."— Presentation transcript:
40 years of quantum chemistry from polywater to the real stuff Ad van der Avoird Nijmegen, 25 April 2008
Water Most abundant compound on the Earth’s surface Principal constituent of all living organisms Subject of longer and more vigorous study than any other substance From: L.C. Allen, The rise and fall of polywater New Scientist, 16 August 1973.
Anomalies of water High boiling point Large heat of vaporization Solid (ice) floats on liquid (water) Ice has many different phases Liquid density maximum at 4°C Compressibility decreases with increasing T up to 46.5°C Large specific heat C p with minimum at 36°C Large dielectric constant High surface tension (highest except metals)
Polywater, also called “anomalous water” Freezing point −40 ◦ C Boiling point >150 ◦ C Density 1.4 g/cm 3 High viscosity 1962 Discovered by N. Fedyakin, Sovjet Union Then studied by B. Deryagin et al., Moscow 1966 Discussion of the Faraday Society 1966-1972Intensive studies in UK, USA
“There are several ways in which certain liquids can crystallize—can freeze— several ways in which their atoms can stack and lock in an orderly, rigid way. Suppose that the sort of ice we skate upon and put into highballs—what we call ice-l—is only one of several types of ice. Suppose water always froze as ice-l on Earth because it never had a seed to teach it how to form ice-two, ice-three, ice-four…? And suppose that there were one form, which we will call ice-nine, a crystal as hard as this desk with a melting point of 130°F. And suppose that one Marine had with him a tiny capsule containing a seed of ice-nine, a new way for the atoms of water to stack and lock, to freeze. If that Marine threw that seed into the nearest puddle…?” “The puddle would freeze?” I guessed. “And all the muck around the puddle?” “It would freeze.” “And all the puddles in the frozen muck? They would freeze?” “You bet they would, and the United States Marines would rise from the swamp and march on.” Cat’s cradle (Kurt Vonnegut, 1963):
“There is such stuff?” “No, no, no, no... if you'd been listening to what I have been trying to tell you about pure research men, you wouldn't ask such a question. Pure research men work on what fascinates them, not on what fascinates other people.” “If the streams flowing through the swamp froze as ice-nine, what about the rivers and lakes the streams fed?” “They'd freeze.” “And the oceans the frozen rivers fed?" “They'd freeze, of course.” “And the springs feeding the frozen lakes and streams, and all the water underground feeding the springs?” “They'd freeze, damn it!” “And the rain?” “When it fell, it would freeze into hard little hobnails of ice-nine and that would be the end of the world.”
Tetrahedral hydrogen bonded network in normal water
Structure of polywater (ice-nine) Each H atom is shared by two O atoms, no distinction between OH bonds and hydrogen bonds
E.R. Lippincott et al., Science 164, p. 1482 (1969) Infrared and Raman spectra completely different from normal water K. Morokuma, Chem. Phys. Lett. 4, p. 358 (1969) L.C. Allen, P.A. Kollman, Science 167, p.1443 (March 1970) “Explained” properties by quantum chemistry (semi-empirical CNDO calculations) L.C. Allen, P.A. Kollman, J. Am. Chem. Soc. 92, p. 4108 (July 1970) Presented evidence that polywater does not exist (ab initio calculations)
End of polywater story: 1973 Special properties caused by solution of various impurities from capillary walls What could be learned? Role of media: popular journals, newspapers (fear of ice-nine) What is “New York Times physics”? Sociology of scientist world How efficient the scientific method can be (L.C. Allen)
Structure, motion, and properties of water are determined by energy landscape (potential surface, force field, forces between the molecules)
Can be determined by quantum chemistry ab initio calculations required First ab initio calculated water potentials: Popkie, Kistenmacher, Clementi (IBM) J. Chem. Phys. 59, 1325 (1973) Hartree-Fock calculations, 190 points Matsuoka, Clementi, Yoshimine (IBM) J. Chem. Phys. 64,1351 (1976) Configuration-Interaction calculations, 66 points
2007 / 2008 New ab initio water potential: CC-pol Based on > 2500 CCSD(T) points extrapolated to CBS limit at MP2 level Analytic representation, correct long-range behavior Polarizable, includes many-body polarization effects Supplemented with 3-body exchange terms Tested by spectroscopy on dimer and trimer Used in MD simulations for liquid water
Water cluster spectra (far-infrared, high resolution) from R.J. Saykally group (UC Berkeley) and from W.L. Meerts et al. (Nijmegen)
How to use of water cluster spectra to test potential surfaces? Pair potential Dimer quantum levels Dimer spectrum Pair + 3-body potential Trimer quantum levels Trimer spectrum Compare with experimental spectra
Quantum tunneling Double well potential Energy levels Wave functions
Water dimer Hydrogen-bonded equilibrium structure
Conclusion CC-pol, with the accompanying many-body interaction model, is the first universal water force field: good for the dimer and trimer, as well as for liquid water R. Bukowski, K. Szalewicz, G.C. Groenenboom, A.van der Avoird Science, 315, 1249 (2007) J. Chem. Phys. 128, 094313, 094314 (2008) + unpublished
After 40 years Complete set of maps of the water energy landscape is now available Quantum chemistry can be trusted to make accurate predictions, not only for water (in the hands of experts)
Cat’s cradle (Kurt Vonnegut, 1963) “See the cat? See the cradle?” “It’s just an illusion!” 2007 † A cat's cradle is nothing but a bunch of X's between somebody's hands, and little kids look and look and look at all those X's, but there's no damn cat, and no damn cradle.
Your consent to our cookies if you continue to use this website.