Intermolecular perturbation theory IMPT

As might be expected, the results of analyses that separate these terms as stringently as possible, such as Hayes and Stone s intermolecular perturbation theory (IMPT) [44], which uses a procedure [45] in which the difference between monomer and dimer basis sets is used to apportion induction (= polarization) and donor-acceptor contributions. Stone and Misquitta [46] point out that using this definition, the donor-acceptor energy would vanish if a complete basis set were used. The observed dependence for the water dimer is shown in Figure 18.6. 

If we have to use non-orthogonal wavefunctions, then the natural one-electron orbitals in which to express them are the SCF molecular orbitals of the non-interacting molecules. From these we can construct antisymmetrized (determinantal) wavefunctions in which some orbitals of each molecule are occupied. Because of the non-orthogonality of the orbitals, these determinant al wavefunctions will also be non-orthogonal. It is possible to construct a perturbation theory in which the wavefunction is expanded in terms of these determinants. Fortunately it is possible to formulate it in such a way that the separation of the Hamiltonian into an unperturbed part and a perturbation is unnecessary. The resulting Intermolecular Perturbation Theory (IMPT) has been incorporated into the Cambridge Analytical Derivatives Package (CADPAC)i ... 

All the methods discussed above have the property of being formulated in a completely basis set independent way. Another possible approach is to consider the Schrddinger equation in the matrix form using some specific basis set. If this matrix is decomposed appropriately, one can obtain a family of so-called symmetric perturbation treatments [19,67]. The best known of these is the variant called intermolecular perturbation theory (IMPT) developed by Hayes and Stone, which has led to many successful applications in the many-electron context [73-76]. 

For Inter Molecular Perturbation Theory (IMPT) see Hayes, I. C. Stone, A. J. An intermolecular perturbation theory for the region of moderate overlap, Mol. Phys. 1984, 53, 83-105 papers of this kind, however, contain a large amount of theoretical and mathematical detail and are not transparent to the uninitiated. For Symmetry-Adapted Perturbation Theory (SAPT) see e.g. Bukowski, R. Szalewicz, K. Chabalovski, C. F. Ab initio interaction potentials for simulations of dinitramine solutions in supercritical carbon dioxide with cosolvents, J. Phys. Chem. 1999, A103, 7322-7340, and references therein. The Morokuma decomposition scheme is described in Kitaura, K. Morokuma, K. A new energy decomposition scheme for molecular interactions within the Hartree-Fock approximation, Int. J. Quantum Chem. 1976,10, 325-340. 

CCDC = Cambridge Crystallographic Data Centre CIF = crystallographic information file CSD = Cambridge Structural Database IMPT = intermolecular perturbation theory PC A = principal-components analysis PDB = Brookhaven Protein Data Bank SQP = square-planar pyramid TBP = trigonal bipyramid. 

EL-HAV = Eisenschitz, London-Hirschfelder, Amos, Van der Avoird FORS = fully optimized reaction space IMPT = intermolecular perturbation theory JS = Jeziorski-Kolos LCD = localized charge distribution MK = Morokuma-Ki-taura MS-MA = Murrell. Shaw-Musher, Amos RS-PT = Rayleigh-Schrodinger perturbation theory RVS = reduced variational space SA = symmetry-adapted perturbation theory SNOPT = symmetric non-orthogonal perturbation theory SRS = symmetrized Rayleigh-Schrddinger. 

Many of Coulson s qualitative ideas about the energy components of the binding energy had their theoretical footing in IMPT (see Intermolecular Interactions by Perturbation Theory). IMPT is almost as old as quantum mechanics itself, starting with the seminal work of Eisenschitz and London in 1930, and there are many variants. Here we present a very short... 

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