THEORETICAL STUDY OF THE STRUCTURES AND ENERGETICS OF AROMATIC CLUSTERS: DEVELOPMENT OF RELIABLE AND PRACTICAL THEORETICAL MODELS FOR INTERMOLECULAR POTENTIALS
Moller-Plesset second order perturbation theory (MP2) has proven to be one of the most cost-effective methodologies for calculating the intermolecular potentials of clusters of aromatic molecules. Despite its popularity, there still remains uncertainty regarding the reliability of MP2 in the prediction of thermochemical properties of weakly bound complexes, such as van der Walls clusters of aromatic molecules. This situation gets complicated by the fact that binding energies computed by the supermolecular approach tend to overestimate the true binding energy due to the so-called basis set superposition error (BSSE), which arises from an unbalance in the monomers' basis sets. In this work, we discuss a systematic procedure to extract the different sources of errors in the calculation of binding energies for aromatic clusters by MP2 theory. We apply this procedure to the case of benzene dimer and discuss its application in the study of other types of clusters. Given the significant computational expense incurred in the calculations involving correlated methods such as MP2, we have developed and validated a simplified methodology, the Hartree-Fock Dispersion (HFD), where the dispersion forces are included in the Hartree-Fock Hamiltonian in the form of a simple London dispersion term added in a perturbative manner. We have been able to improve and extend the HFD methodology to study the dynamics of the vdW interactions in aromatic clusters, through the interface of the ab initio molecular dynamics method atoms-centered basis functions and density matrix propagation (ADMP) with the HFD model, in order to give a reasonable interpretation of the experimental data. We present our work on ab initio molecular dynamics simulations of the benzene dimer to solve the discrepancies concerning the minimum energy configuration.
School:The University of Akron
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:benzene dimer mp2 calculations ab initio molecular dynamics counterpoise method basis set superposition error
Date of Publication:01/01/2006