Ede Kapuy

Application of the many-body perturbation theory to normal saturated hydrocarbons in the localized representation

The second-order energy corrections are calculated for some normal saturated hydrocarbons by using the many body-perturbation theory (MBPT) based on localized orbitals. The correlation energies are expressed as the sum of contributions from virtual orbital pairs. We have found that these contributions are transferable and have interesting structural features: the trans-coplanar effects are relatively large. Partitioning the correlation energies according to the “order of neighbourhood” we have found that the zero order effects are the largest but the first and second neighbour contributions are also important.

An efficient method for using molecular symmetry: The presence of model geometries

Abstract In a series of papers a new method which uses the molecular symmetry for treatment of extended molecules is investigated. In this paper it is shown that in the presence of model geometries the method — on which a new ab initio program named SYCETY is based — is effective for calculation of large, related systems.

A decomposition of the total energy at the HF-SCF level and at several levels of correlation. III:: A study of the interaction in H2O–AlH2OH+NH3 at the Hartree–Fock self-consistent field level

Abstract The method of separated molecular orbitals (SMO) has already proved to be useful for describing the energy partitioning at the Hartree–Fock (HF) level in several weakly interacting systems. In the present paper, the total energy decomposition into different contributions according to the interacting units is discussed at the HF level for a zeolite model system. The effect of the basis set superposition is considered by the use of SMO in a simple and straightforward manner.

Geometry dependence of the proton affinities in the electronic ground, excited triplet and ionized doublet states of H2CO and H2COH+

Abstract The ionization potential of the closed shell H2CO, H2COH+, H2COH22+ as well as the proton affinity of H2CO and H2COH+ have been studied at a variable CO bond length in the ground singlet and some of the low lying excited triplet and ionized doublet states.