The general Hartree-Fock (GHF) method is a quantum mechanical method for electronic structure calculations that uses a single determinantal wave function with no restrictions on the one-electron orbitals other than orthonormality and the use of a specific basis set. The more familiar restricted Hartree-Fock (RHF) and unrestricted Hartree-Fock (UHF) methods can be regarded as special cases of th...

The quantum Monte Carlo (QMC), CASINO code was run to calculate the ground state energy for the hydrogen molecule. The variational Monte Carlo (VMC) technique was used, employing the unrestricted Hartree-Fock (UHF) method, instead of the restricted Hartree-Fock (RHF) method. By altering the VMC steps in the input parameters of the CASINO code, the best ground state energy for the hydrogen molec...

A generalization of the coupled cluster (CC) singles, doubles, and a hybrid treatment of connected triples [denoted as CCSD(T)-h] [Shen et al., J. Chem. Phys. 132, 114115 (2010)] to the restricted Hartree-Fock (RHF) reference is presented. In this approach, active (or pseudoactive) RHF orbitals are constructed automatically by performing unitary transformations of canonical RHF orbitals so that...

nanopartmles have been used as an approach to improve the pharmacodynamic and phannacokinetie propertiesof various drues. amino acids have been considered to be useful to make such nano particles because ofthocompatithe and biodegradable characteristic. the quantum mechanical method that was chosen to analyze inethio hexa peptide nano ring]. the structure of some peptide nanorrigs as well as th...

We have constructed the unrestricted Hartree-Fock (UHF), restricted Hartree-Fock (RHF), and full configuration interaction (FCI) position and momentum intracules and holes for H···H at bond lengths R from 1 to 10 bohrs. We trace the recently discovered inversion of the UHF position hole at intermediate R to over-localization of the spin-orbitals, and support this by a correlation energy compone...

The self-energy of the Dirac Brueckner-Hartree-Fock calculation in nuclear matter is parametrized by introducing density-dependent coupling constants of isoscalar mesons in the relativistic Hartree-Fock (RHF) approach where isoscalar meson σ , ω and isovector meson π , ρ contributions are included. The RHF calculations with density dependent coupling constants obtained in this way not only repr...

We propose a method to locate the solutions to the self-consistent field (SCF) equations, using an approach based upon metadynamics. We define a distance function between density matrices. Within an SCF calculation, when a solution is found, a biasing potential based on distance from the solution is added to the energy to avoid reconvergence to the same solution. Multiple solutions can therefor...

In this article, we set up a functional setting for mean-field electronic structure models of Hartree-Fock or Kohn-Sham types for disordered crystals. The electrons are quantum particles and the nuclei are classical point-like particles whose positions and charges are random. We prove the existence of a minimizer of the energy per unit volume and the uniqueness of the ground state density of su...

The vibrational frequencies for the fundamental modes and the energies of low lying states of alanine in neutral and its zwitterionic form in gas phase have been calculated at RMP2 ab-initio level. The results so obtained have been compared with earlier theoretical calculations and experimental observations of IR and RAMAN spectrum. In the present study, it has been observed that our results ar...

In agreement with our previous work [A. Kalemos, J. Chem. Phys. 138, 224302 (2013)], we established the centrosymmetric nature of the ground BNB state by means of the Restricted Coupled Cluster Singles and Doubles + Perturbative Triples (RCCSD(T)) computational method. We have also studied the symmetry adapted or broken behavior at the Configuration Interaction Singles and Doubles (CISD), CISD ...