Final program

Monday 26 April 2004, SISSA, Lecture room "D" 11.30-12.45 Krzysztof SZALEWICZ (University of Delaware) Spectroscopic predictions for clusters and nanodropletes based on ab initio potentials (abstract) 12.45-13.00 Discussion 13.00-14.00 --- Lunch break --- 14.00-14.45 Saverio MORONI (INFM Democritos and Univ. of Rome "La Sapienza") Computational spectroscopy of doped Helium clusters 14.45-15.30 Discussion Tuesday 27 April 2004, SISSA, Lecture room "D" 11.30-12.45 Krzysztof SZALEWICZ (University of Delaware) Perturbation theory of intermolecular interactions based on density-functional description of monomers (abstract) 12.45-13.00 Discussion 12.45-13.00 --- Lunch break --- 14.00-14.30 Stefano BARONI (INFM Democritos and SISSA Trieste) Coping with the missing Divine Functional: a practical proposal for a seamless joint between standard DFT calculations and asymptotic estimates of electronic correlations based on linear response 14.30-15.00 Anton KOKALJ (Josef Stefan Istitute Ljubljana and INFM Democritos) Deprotonation of methane on Rh(111): an example of weak molecule--surface interaction 15.00-15.30 Tiffany WALSH (University of Warwick) Toward reliable calculation of molecular physisorption on metal surfaces 15.30-16.00 General discussion Wednesday 28 April 2004, SISSA, Lecture room "A" 14.30-15.45 Krzysztof SZALEWICZ (University of Delaware) Can many-body expansion be truncated in simulations of liquids? (abstract) 16.00-16.30 Raffaele RESTA (INFM Democritos and Univ. of Trieste) Static and dynamic multipoles in molecular fluids: The case of liquid water 16.30-17.00 Sandro SCANDOLO (ICTP Trieste and INFM Democritos) Effective N-body potentials for ionic liquids 17.00-17.30 General discussion

ABSTRACTS of K. Szalewicz

Spectroscopic predictions for clusters and nanodropletes based on ab initio potentials
As recently as ten years ago, there existed very few reliable ab initio computed potentials for interactions between molecules. Developments in computer power and in quantum chemical software changed this state to the point that for smaller systems ab inito potentials are usually more accurate than empirical ones. Among ab initio methods,symmetry-adapted perturbation theory (SAPT) [1] is often the method of choice as it provides not only accurate values of interaction energies but allows physical interpretation of these energies in terms of electrostatic, induction, dispersion, and exchange interactions. The SAPT method will be briefly described first, followed by presentations of applications to various small clusters. One of the smallest possible clusters is the helium dimer. The thermophysical predictions based on the 1997 SAPT potential for this system have become a standard for apparatus used to measure the thermal conductivity and viscosity of gases. Recent improvements of this potential [2] will be described including the first calculation of the relativistic corrections that become relevant at the current level of accuracy. Next, theoretically predicted spectra of several small clusters [3-7], in particular containing the helium atom as one of the monomers, will be presented and compared with experiments. Due to the high accuracy of such experiments, these comparisons offer the most stringent tests of ab initio potentials. Examples will be given of some first-principle predictions for these systems that may be more accurate than values inferred from spectral data. Finally, ab initio potentials for systems containing helium can be used to investigate solvation in superfluid helium nanodroplets and such applications will be discussed.

1. B. Jeziorski and K. Szalewicz "Symmetry-Adapted Perturbation Theory", in "Handbook of Molecular Physics and Quantum
2. W. Cencek, M. Jeziorska, R. Bukowski, M. Jaszunski, B. Jeziorski, and K. Szalewicz "Helium Dimer Interaction Energies from Gaussian Geminal and Orbital Calculations", J. Phys. Chem. A, DOI 10.1021/jp037544i (2004).
3. O. Akin-Ojo, R. Bukowski, and K. Szalewicz "Ab Initio Studies of He-HCCCN Interaction", J. Chem. Phys. 119, 8379 (2003).
4. B.T. Chang, O. Akin-Ojo, R. Bukowski, and K. Szalewicz "Potential Energy Surface and Rovibrational Spectrum of He-N2O Dimer", J. Chem. Phys. 119, 11654 (2003).
5. G. Murdachaew, K. Szalewicz, H. Jiang, and Z. Bacic "Intermolecular potential energy surface and spectra of He--HCl complex from ab initio symmetry-adapted perturbation theory calculations", J. Chem. Phys., submitted.
6. K. Patkowski, T. Korona, R. Moszynski, B. Jeziorski, and K. Szalewicz "Ab initio potential energy surface and second virial coefficient for He-H2O complex", J. Mol. Str. (Theochem), 591, 231-243 (2002).
7. G.C. Groenenboom, P.E.S. Wormer, A. van der Avoird, E.M. Mas, R. Bukowski, and K. Szalewicz "Water Pair Potential of Near Spectroscopic Accuracy: II. Vibration-Rotation-Tunneling Levels of the Water Dimer", J. Chem. Phys. 113, 6702 (2000)

Perturbation theory of intermolecular interactions based on density-functional description of monomers
Applications of wave-function-based ab initio methods to interactions of molecules containing ten or more atoms have not been possible since calculations employing symmetry-adapted perturbation theory (SAPT) or any other electronic structure method that includes correlation effects at a level adequate for describing intermolecular interactions require relatively significant computer resources. On the other hand, although the existing density-functional theory (DFT) are fast enough for such calculations, these methods are known to fail to describe an important part of the van der Waals forces, the dispersion interaction. In fact, we have shown [1] that supermolecular DFT calculations lead to large errors also in other interaction energy components (the electrostatic, induction, and exchange interactions) due to an incorrect behavior of electron densities at distances from nuclei that are relevant for intermolecular interactions. We have recently shown that a solution to this difficulty is a SAPT approach utilizing the DFT description of monomers [1,2]. The method does not relay on asymptotic expansions and therefore is applicable for all separations between the interacting molecules. The SAPT(DFT) approach avoids the problems of supermolecular DFT by using this method only to describe each monomer, but calculating the interaction energies from expressions beyond DFT. In addition, the wrong long-range behavior of monomer densities is fixed by applying an asymptotic correction to the exchange-correlation potential of DFT. SAPT(DFT) calculations require only a small fraction of computer resources used by the regular SAPT and converge much faster in the size of the basis sets. Moreover, although initially SAPT(DFT) was expected to be a method providing medium quality results for very large molecules, it turned out that at least in some cases the accuracy of SAPT(DFT) surpasses that which can be reached with the currently programmed regular SAPT and reasonable size basis sets. Our most recent results for several dimers show that in all cases when there were significant discrepancies between the results from the two approaches, these were resolved in favor of SAPT(DFT), i.e., were resulting from theory level truncations and basis set incompleteness in the regular SAPT calculations.

1. A.J. Misquitta and K. Szalewicz, Chem. Phys. Lett. 357, 301 (2002).
2. A.J. Misquitta, B. Jeziorski, and K. Szalewicz, Phys. Rev. Lett. 91, 033201 (2003).

Can many-body expansion be truncated in simulations of liquids?
The total interaction energy of a cluster or an ensemble of molecules in a Molecular Dynamics (MD) or Monte Carlo (MC) simulation is a sum of pair interaction and three-, four-body, etc. nonadditive interactions. One of the fundamental questions in this field is how many terms in this expansion are needed for reasonably accurate predictions of the properties of these systems. The pair interactions and three-body nonadditive interactions can be computed using symmetry-adapted perturbation theory (SAPT) and the system of computer codes named SAPT2002 [1]. This approach has provided some of the most accurate intermolecular potentials for various dimers and trimers, as confirmed by comparisons of the computed spectra with experiment. In particular, the water dimer and trimer spectra agreed with experiment very well [2]. Simulations of liquid water with SAPT potentials [3,4] determined quantitatively the role that the three-body effects play in this system. Recently, the many-body expansion was applied to analyze the Car-Parrinello type MD simulations for water. This approach always evaluates the complete N-body potential in each step using a density-functional theory (DFT) approach. Using the same DFT method, we have computed two-body and three-body potentials and fitted them by a similar analytic form as used in the SAPT fits. The resulting 2+3-body potential can be used in simulations at a fraction of the cost of the simulations with the N-body potential. The results of these simulations will be presented, which constitute a numerical test of the convergence of the many-body expansion for water and answer the question set above. The analysis of the simulations with the DFT potential and comparisons with the SAPT potential provided also important insights into sensitivity of simulations to various regions of the potential, resulting in an improved SAPT potential. Even more importantly, it led to a better understanding of the mechanism of the formation of hydrogen bond network in water.

1. "SAPT2002: An Ab Initio Program for Many-Body Symmetry-Adapted Perturbation Theory Calculations of Intermolecular Interaction Energies" by R. Bukowski et al., University of Delaware and University of Warsaw: http://www.physics.udel.edu/~szalewic/SAPT/SAPT.html
2. G.C. Groenenboom, E.M. Mas, R. Bukowski, K. Szalewicz, P.E.S. Wormer, and A. van der Avoird, Phys. Rev. Lett. 84, 4072 (2000).
3. E.M. Mas, R. Bukowski, and K. Szalewicz, J. Chem. Phys. 118, 4386 (2003).
4. E.M. Mas, R. Bukowski, and K. Szalewicz, J. Chem. Phys. 118, 4404 (2003).