Study Hydrogen Bonds Quantum Chemistry Methods Density Functional Theory

Author(s)

Eduardo Augusto Rissi

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2004-05-31

Examining board members

Sylvio Roberto Accioly Canuto; Lucy Vitoria Credidio Assali; Klaus Werner Capelle; Jose Rachid Mohallem; Fernando Rei Ornellas

• Advisor: Sylvio Roberto Accioly Canuto

Abstract

Hydrogen bonding is a topic of interest in the scientific community since the end of the XIX century. Its importance is enormous in processes related to life as, for example, the stabilization of DNA structures and the maintenance of water in its liquid state. Several theoretical methodologies were developed to study molecular systems and hydrogen bonds, among them is the use of many-body perturbation theory (MBPT). An alternative to MBPT, that has gained confidence, is the employment of the density functional theory (DFT). In the present thesis we calculate properties of hydrogen-bonded systems in clusters and liquids using both methodologies, DFT and MBPT. Among the properties considered are rotational constants, dipole moments, biding energies, spectroscopic shifts upon complex formation and light scattering. Part of this thesis is dedicated also to point out the difference between the properties of an optimized cluster and a liquid structure generated by Monte Carlo simulation. We compare the results obtained for the urea-water complex in these two situations and reinforce the fact that liquid and cluster are different physical situations, whose properties are also different. The systems studied were HCN, CH IND.3CN, HC IND.3N, HC IND.2NC, HCN H IND.2O and (NH IND.2)IND.2CO H IND.2O. from the results obtained in this thesis, we verify that DFT is indeed feasible to obtain properties of hydrogen bonded molecules and biomolecules. (AU)