Cornelia Kozmutza

Calculation of the dispersion interaction energy by using localized molecular orbitals

In this paper, we present a method for the calculation of dispersion interaction energies of molecules, which is based on the localized molecular orbitals of the supermolecule. It is shown (using various basis sets) that the energy contributions of the localized molecular orbitals, for distances around the intermolecular energy minimum, are transferable to a fairly good approximation from the noninteracting monomers to the supermolecule. The correlation energy component of the interaction energy can be separated into inter‐ and intraparts. We show how the basis set superposition errors can be located and separated at the correlated level. Results are presented for several systems [(H2O)2, (NH3)2, and Ne2 ] with different basis sets from the minimal one to the split shell plus polarization functions. The method applies the well‐known Boys’ localization procedure and has the advantage that for the dispersion energy at a given geometry, the integral transformation should only be carried out once (from the ba...

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.

A study of weakly interacting systems in localized representation, including the many-body effect

The method of the separated molecular orbitals (SMOs), as a version of the localized representation is discussed as a useful tool for studying weakly interacting systems. As to the Hartree-Fock level, the contributions of the atomic basis sets in some dimers and their counter-poise (CP) corrected systems are compared. The results suggest, that using SMOs the validity of the CP recipe can be demonstrated. The localized many-body perturbation theory (LMBPT) incorporating the method of SMOs makes it possible to study the van der Waals type systems at several levels of correlation. This allows using the SMO-LMBPT scheme for discussing not only the two-body but the many-body interaction energy quantities as well. As an example, the results obtained for the three-body interaction energies in some He-clusters are given. These results show that the three-body effects are negligible in comparison to the two-body ones, the relative significance of the charge-transfer components, on the other hand, are important.

The application of localized representation in the calculation of interaction energy

Abstract The results presented in this paper for the dimer of H2O as well as for the dative complexes formed by the interaction of BH3 + H2O and AlH3 + H2O suggest that about 50% of the dispersion energy can be recovered, using a 6-31G(d) basis set, in cases when only the contributions of those localized molecular orbitals are included which are in the vicinity of the interaction region. The reduction in computing time is about an order of magnitude. The procedure applied makes it possible to avoid basis set superposition errors at the correlated level. The method presented opens the way for studying large clusters containing various atoms beyond the HF level.

To address accuracy and precision using methods from analytical chemistry and computational physics

In this work the pesticides were determined by liquid chromatography–mass spectrometry (LC-MS). In present study the occurrence of imidacloprid in 343 samples of oranges, tangerines, date plum, and watermelons from Valencian Community (Spain) has been investigated. The nine additional pesticides were chosen as they have been recommended for orchard treatment together with imidacloprid. The Mulliken population analysis has been applied to present the charge distribution in imidacloprid. Partitioned energy terms and the virial ratios have been calculated for certain molecules entering in interaction. A new technique based on the comparison of the decomposed total energy terms at various configurations is demonstrated in this work. The interaction ability could be established correctly in the studied case. An attempt is also made in this work to address accuracy and precision. These quantities are well-known in experimental measurements. In case precise theoretical description is achieved for the contributing monomers and also for the interacting complex structure some properties of this latter system can be predicted to quite a good accuracy. Based on simple hypothetical considerations we estimate the impact of applying computations on reducing the amount of analytical work.

Ab initio program for treatment of related systems. Transferable quantities of localized molecular orbitals

Abstract It is well known that transferability is an important property for the investigation of related systems. In cases when one can define quantities for molecular parts, which are additive and transferable, certain similarities of different molecules can be simply recognized. One-electron properties, as electric moments or kinetic energy contributions derivable from transferable/localized molecular orbitals, are especially useful for the above purpose. In this paper we demostrate, that these quantities are convenient for studying not only extended molecules, but weakly interacting systems as well.

A decomposition of the total energy at the HF-SCF level and at several levels of correlation: IV. A study of the interaction in H2O-AlH2OH + NH3 at the correlated level

Abstract The method of separated molecular orbitals (SMOs) combined with the localized many-body perturbation theory (LMBPT) has already proved useful for partitioning the energy at several levels of correlation in various weakly interacting systems. The energy decomposition into different contributions according to the interacting units is discussed for a zeolite model system in the present paper. The effect of basis set superposition is also considered, using the SMO–LMBPT scheme.

Solvent-assisted interaction between molecules: calculations at the Hartree-Fock + correlation level Part 1. The study of the BH3 + H2O and NH3 + NH3 systems

Abstract The dispersion interaction energy with the molecules BH3 and NH3 was computed using a specific supermolecule method. The essence of the approach used lies in applying a localized representation in the virtual space. This method makes it sensible to investigate the above systems surrounded by several water molecules.

On the use of spatial symmetry in ab initio calculations. Transformation of the two-electron integrals from atomic orbital to localized molecular orbital basis

Anm5-dependent integral transformation procedure from atomic orbital basis to localized molecular orbitals is described for spatially extended systems with some Abelian symmetry groups. It is shown that exploiting spatial symmetry, the number of non-redundant integrals for normal saturated hydrocarbons can be reduced by a factor of 2.5-3.5, depending on the size of the system and on the basis. Starting from a list of integrals over basis functions in canonical order, the number of multiplications of the four-index transformation is reduced by a factor of 2.8-3.5 as compared to that of Diercksens algorithm. It is pointed out that even larger reduction can be achieved if negligible integrals over localized molecular orbitals are omitted from the transformation in advance.