DMC and VMC Calculations of the Electric Dipole Moment and the Ground-State Total Energy of Hydrazine Molecule Using CASINO-Code

Abstract

In this study quantum Monte Carlo (QMC) calculations of the electric dipole moment and ground-state total energy of hydrazine (N₂H₄) molecule using CASINO-code is presented. By employing the restricted Hartree-Fock (RHF) scheme, two QMC techniques were used in this work: variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC) techniques. The optimization of the Slater-Jastrow trial wave-function was done using variance-minimization scheme. The simulations require that the configurations must evolve on the time scale of the electronic motion, and after equilibration, the estimated effective time-step be obtained. In this study, the electric dipole moment of N₂H₄ molecule was calculated using only the DMC technique. The result obtained gives an electric dipole moment value of 2.0 D, which is in good agreement with the experimental value of 1.85 D.

Similarly, the ground-state total energy of N₂H₄ molecule was calculated using both VMC and DMC methods. It was observed that the result obtained from the VMC technique agrees very-well with the best theoretical value while the DMC technique gave a ground-state total energy value lower than all other theoretical values in literature, suggesting that the DMC result –111.842774 ± 0.00394 a.u., should be the exact ground-state total energy of hydrazine molecule. However, the results from this study are found to be precisely approaching the required order of chemical accuracy.

Keywords: Hydrazine (N₂H₄), QMC, VMC, DMC, CASINO-Code.