Development of new approximations for ab initio simulations

Author(s)

Luana Sucupira Pedroza

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2010-12-14

Examining board members

Antonio Jose Roque da Silva; Alex Antonelli; Paulo Barbeitas Miranda; Helena Maria Petrilli; Marcio Teixeira do Nascimento Varella

• Advisor: Antonio Jose Roque da Silva

Abstract

Computer simulations are essential tools for a microscopic understanding of many processes that occur in nature. In particular, ab initio simulations, i.e., first principles simulations, can predict new properties and support experimental results, without the need to use empirical potentials which are fitted for a specific configuration of the system. However, even in ab initio simulations it is necessary to do approximations for the electronic structure calculations and for the description of the nuclear movements. In this thesis, new approximations for the exchange-correlation energy functional of Density Functional Theory (DFT) are proposed and tested for atoms, molecules and solids. The description of the nuclear movements was done using the Monte Carlo technique, however the total energy calculations were obtained by DFT. We also propose a new methodology which allows the description of intramolecular movements whose vibrational frequencies can not be treated classically. As an illustration, we have studied water clusters and liquid water, showing the relevance of this new methodology on the description of structural, vibrational and of the dipole moment of these systems. (AU)