Many-body Rayleigh-Schrodinger Perturbation Theory Research Articles

Correlation energies in open shell systems. Comparison of CEPA, PNO-CI and perturbation treatments based on the restricted Roothaan-Hartree-Fock formalism

A set of simple molecules in closed and open-shell ground states is treated by the three techniques mentioned in the title, using the same geometries and basis sets (DZ + P). It is found that for nearly all molecules treated in this study (exceptions are H2 and CH3) consistently about 98% of the CEPA valence shell correlation energy is obtained by third-order many-body Ray-leigh-Schrodinger perturbation theory (MB-RSPT). The CEPA and MB-RSPT results for reaction energies and barrier heights for some simple reactions differ by 0 to 30 kJ/mol, the CEPA results being in most cases closer to experiment than MB-RSPT, while CI results are much less reliable as long as CI is limited to singly and doubly substituted configurations only.

Correlation energy in triplet states comparison of many-body perturbation theory and configuration interaction for CH 2 and O 2

Many-body Rayleigh-Schrodinger perturbation theory in the restricted MO formalism through third order and configuration interaction covering all singly and doubly excited states were applied to the lowest triplet states of the methylene and oxygen molecules. The correlation energies given by the two methods for methylene are close in absolute value

Correlation energy in triplet electronic states. Application of the many-body Rayleigh-Schrödinger perturbation theory in the restricted Roothaan-Hartree-Fock formalism

Explicit formulas over orbitals are given for the correlation energy in triplet electronic states of atoms and molecules. The formulas were obtained by means of the diagrammatic many-body Rayleigh-Schrodinger perturbation theory through third order assuming a single determinant restricted Roothaan-Hartree-Fock wave function. A numerical example is presented for the NH molecule.

On the use of UHF orbitals in ionization energy calculations

The UHF Hamiltonian and simple Lowdin-like annihilators are formulated in the second quantization formalism. The so formulated Hamiltonian was employed in many-body Rayleigh-Schrodinger perturbation theory to evaluate the corrections to the UHF orbital energies.

Calculation of vertical ionization potentials of H2O and Ne by many-body Rayleigh-Schrödinger perturbation theory

The vertical ionization potentials of H2O and Ne are calculated by many-body Rayleigh-Schrodinger perturbation theory up to third order. The comparison of the present method with the other approaches is done.

Quasi-degenerate many-body Rayleigh-Schrödinger perturbation theory

Starting from the Hugenholtz diagrammatic technique (resolvent operator and factorization theorem with complex convolution) a quasi-degenerate many-body Rayleigh-Schrodinger perturbation theory is derived. This derivation is based on an algebraic similarity between the formal generalized characteristic problem and its many-body version. Diagrammatic expressions for the perturbed state vectors and mean values of an observable are obtained. The connection between our method and the folded-diagram approach is discussed.