This paper aims at determining the total energy and bond lengths of some polyatomic organic molecules, using quantum Monte Carlo (QMC) CASINO-code. The QMC code employed the VMC and DMC methods in the computations with emphasis on DMC, and using Slater-Jastrow trial wave-function formed from Hartree-Fock orbitals. The calculated results show that our reported values are in good agreement with the experimental values of both Hehre et al., and Linus Pauling. The total energies obtained in this study are 6 significant figures more accurate than those of previous studies.

Quantum Monte Carlo (QMC) calculations of the electric dipole moment and ground-state total energy of hydrazine (N2H4) molecule using CASINO-code have been carried-out by employing the VMC and 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; and a value of 2.0D which is in good agreement with the experimental value of 1.85D was obtained. On the other hand, 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 [17], but the DMC technique gave a ground-state total energy lower than all other theoretical values in literature, suggesting that the DMC result of –111.842774 ± 0.00394 a.u. may be the exact ground-state total energy of hydrazine molecule. The calculated values of electric dipole moment and ground-state total energy in this work are compared with the available experimental values and the values reported by different workers. Reasonably good agreement has been obtained between them in the required order of chemical accuracy.

ABSTRACT. This paper aims at determining the total energy and bond lengths of some polyatomic organic molecules, using quantum Monte Carlo (QMC) CASINO-code. The QMC code employed the VMC and DMC methods in the computations with emphasis on DMC, and using Slater-Jastrow trial wave-function formed from Hartree-Fock orbitals. The calculated results show that our reported values are in good agreement with the experimental values of both Hehre et al., and Linus Pauling. The total energies obtained in this study are 6 significant figures more accurate than those of previous studies.

We have employed a quantum confinement (QC) model to the study of different shapes of nanocrystalline silicon (nc-Si) quantum dot. Each dots (shapes), although within the limits of an effective diameter of 3nm, exhibits divergence leading to different electronic energy based on the transitions from the quantum selection rule. Also, the graphical representation of the energies from each shape as a function of the effective diameter gives a qualitatively similar spectrum of discrete energies. The results obtained in this work using QC model are in good agreement with experiment and other models in literature.

ABSTRACT. We have employed a quantum confinement (QC) model to the study of different shapes of nanocrystalline silicon (nc-Si) quantum dot. Each dots (shapes), although within the limits of an effective diameter of 3nm, exhibits divergence leading to different electronic energy based on the transitions from the quantum selection rule. Also, the graphical representation of the energies from each shape as a function of the effective diameter gives a qualitatively similar spectrum of discrete energies. The results obtained in this work using QC model are in good agreement with experiment and other models in literature.