It is known that the ground states of organic conductors have a diversity reflecting the spatial arrangement of the constituent molecules within the unit cell. A systematic theoretical search for the unifying view behind such possible ground states has been made based on the Hartree-Fock mean field approximation not only to the onsite but also to intersite Coulomb interactions with special emph...

The relation between the correlation energy and the entanglement is analytically constructed for the Moshinsky’s model of two coupled harmonic oscillators. It turns out that the two quantities are far to be proportional, even at very small couplings. A comparison is made also with the 2-point Ising model.

Our previously developed constrained-pairing mean-field theory (CPMFT) is shown to map onto an unrestricted Hartree-Fock (UHF) type method if one imposes a corresponding pair constraint to the correlation problem that forces occupation numbers to occur in pairs adding to one. In this new version, CPMFT has all the advantages of standard independent particle models (orbitals and orbital energies...

We develop a systematic way to determine an effective nuclear charge ZD R such that the Hartree– Fock results will be significantly closer to the exact energies by utilizing the analytically known large-D limit energies. This method yields an expansion for the effective nuclear charge in powers of (1/D), which we have evaluated to the first order. This first order approximation to the desired e...

The theory of spin-restricted Brueckner orbitals for high-spin open-shell coupled-cluster wavefunctions is presented. The orbitals are based on single-excitation amplitudes constructed using the symmetric spin–orbital basis coupled-cluster method of Jayatilaka and Lee. It is shown how this approach may be easily implemented within existing open-shell coupled-cluster programs. The method’s perfo...

The charge renormalization procedure for the calculation of the correlation energy of atoms utilizing the analytically known large-D limit solutions for the exact and Hartree–Fock equations is extended to diatomic molecules. This procedure is based on the variation of the nuclear charge, Z , and internuclear distance, R , of the Hartree–Fock Hamiltonian such that the Hartree–Fock energy will be...

The standard Hartree–Fock approximation of the O(N)−invariant φ model suffers from serious renormalization problems. In addition, when the symmetry is spontaneously broken, another shortcoming appears in relation to the Goldstone bosons: they fail to be massless in the intermediate states. In this work, within the framework of out–of– equilibrium Quantum Field Theory, we propose a class of syst...

The phase diagram of the Schwinger model on the lattice with one and two degenerate flavours of Wilson fermions is investigated in the Hartree-Fock approximation. In case of a single flavour (not directly amenable to numerical simulation), the calculation indicates the existence of the parity violating phase at both weak and intermediate-to-strong couplings. In the broken phase, the Hartree-Foc...

The phase diagram of the Schwinger model on the lattice with one and two degenerate flavours of Wilson fermions is investigated in the Hartree-Fock approximation. In case of a single flavour (not directly amenable to numerical simulation), the calculation indicates the existence of the parity violating phase at both weak and intermediate-to-strong couplings. In the broken phase, the Hartree-Foc...

We describe the implementation of analytical Hartree-Fock gradients for periodic systems in the code CRYSTAL, emphasizing the technical aspects of this task. The code is now capable of calculating analytical derivatives with respect to nuclear coordinates for systems periodic in 0, 1, 2 and 3 dimensions (i.e. molecules, polymers, slabs and solids). Both closed-shell restricted and unrestricted ...