Adaptation of electronic structure methods in calculations of nuclear magnetic resonance properties and internal rotation barriers

Author(s)

Lucas Colucci Ducati

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2010-01-10

Examining board members

Roberto Rittner Neto; Aguinaldo Robinson de Souza; Sérgio Emanuel Galembeck; Roy Edward Bruns; Yoshiyuki Hase

• Advisor: Rogério Custodio; Roberto Rittner Neto

Abstract

The hybrid functional ¿half and half¿ BHandH showed similar accuracy with SOPPA (CCSD) and LR-CCSD ab initio methods on the evaluation of density functionals in spin-spin coupling constants calculations. The variation of E in the studied density functions increased the accuracy of spin-spin coupling constants calculations in most cases, where the 50% value for E in B98 functional led to the most accurate values. The optimization of Huz-IIIsu3-J basis function for P with respect to the spin-spin coupling constants, energy and electric field vector on the nuclei showed the same quality in relation to the original basis set for all tested JPH, JPC and JPP spin-spin coupling constants. However, the new basis set presented the best accuracy for JPC and JPP. The internal rotational barrier of some simple molecules (H2O2, H2S2, N2H4, H3COH, H3CNH2 e C2H6) calculated using G3 and G3CEP methods showed deviations smaller than 0.53 kcal mol and 0.86 kcal mol with respect to experimental data and similar quality in relation to CCSD(T)/aug-cc-pVTZ level of theory. The G3 and G3CEP energy components showed that MP4/6-31G(d) or MP4/CEP-31G(d) energy is refined following the sequence: DEG3Large > DE2df,p > DE+ > DEQCI. The relative energy is sensitive to the diffuse and the polarization functions for molecules which contain lone pairs in the atoms of the rotating bond and show a higher rotation barrier. Molecules presenting just one lone pair or bond pair and showing low rotation barriers depend also on an improvement of basis set by the DEG3Large correction as well as DE2df,p and DE+ corrections (AU)