DFT, RHF and MP2 based study of the thermodynamic, electronic and non-optical properties of DNA nucleobases

Abstract

Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children. In this study, the DNA nucleobases, that is. Adenine (A), Guanine (G), Cytosine(C) and Thymine (T) have been investigated by employing quantum chemical methods calculation. The thermodynamic parameters such as entropy, enthalpy, heat capacity and zero point vibrationional energy, non optical linear properties (dipole moment and mean polarizability) and Mullikan charges were calculated using Restricted Hartree–Fock (RHF), Moller-Plesset Second Order Perturbation Theory (MP2) and Density FuTheory (DFT), B3LYP and LSDA methods with 3- 21G, 3-21+G and 6-31G basis set . In addition, HOMO-LUMO energy gap of each of the molecules was calculated. The high value of HOMO-LUMO energy gap indicates the high stability of the molecules in chemical reaction. Of the four molecules, guanine has the highest value of HOMO- LUMO energy gap which implies that it is the most stable molecule in chemical reaction. The values of the dipole moment obtained were in agreement with the experimental values. For instance, the dipole moment of guanine at B3LYP/6-31G was calculated as 7.2D while the experimental value is 7.1D. Gaussian 03 package was used to perform all the calculations. Results from comparison of the DFT, MP2 and RHF methods shows close results and can be seen to support one another.

Keywords: DNA, Nucleobases, HOMO-LUMO, DFT, RHF and MP2