Electronic Structure of Molecular Liquids

• Grant number: 98/09933-8
• Support Opportunities: Research Projects - Thematic Grants
• Start date: March 01, 1999
• End date: May 31, 2002
• Field of knowledge: Physical Sciences and Mathematics - Physics - Atomic and Molecular Physics
• Principal Investigator: Sylvio Roberto Accioly Canuto
• Grantee: Sylvio Roberto Accioly Canuto
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Pesquisadores principais: Adalberto Fazzio

Abstract

This project addresses to the development of methods, techniques and algorithms for the study of the electronic structure of molecular liquids. One of our basic interests is the solvent effects in molecular properties, structures and spectra. Our methodology combines the use of Monte Carlo simulation and well established quantum mechanical methods for the study of molecular systems. The Monte Carlo method is used to generate the liquid structure and is also used for processes where the time-dependence is not relevant. For those cases with time-dependence, such as fluorescence decays, the method of molecular dynamics must be used. We use a Monte Carlo program that was developed in our own group. In the case of molecular dynamics, we use a program that was developed by one of our collaborators. Among those methods for quantum-mechanical calculations we favor the quantum chemistry a initio methods such as many-body perturbation theory and coupled-cluster methods. An interesting alternative for larger systems is provided by density-functional methods. On of our major interests in the recent past has been the study of solvatochromic shifts in molecular absorption spectrum in the visible and UV region. We have recently developed with success a sequential classical-statistic and quantum mechanical methods for the study of these solvatochromic shifts. This procedure requires a rationalization of the intermolecular forces involved between the chromophore (solute) and the solvent molecules. As a natural consequence of those studies we are now interested in extending this approach to study molecular systems of biological interest as well as disordered systems in general. Disordered, here, means both a molecular liquid as well as an amorphous semiconductor. The possibility of studying biomolecules from a quantum-mechanical point of view may lead to a quantum biophysics where important bimolecular processes are studied with the electronic structure explicitly included. Topics that we recently studied such as hydrophobic effects, hydrogen bonding and molecular stability due to a solvent, to mention a few, are of great importance in biophysics such as the case of enzymatic activities. Our approach, though still limited, clearly allows more systematic, and quantum-mechanical, studies of inhibitors, a complex topic also considered in this project. (AU)