Msller-Plesset perturbation calculations (MPn) up to fiftieth order, within both the restricted (RHF) and unrestricted Hartree-Fock (UHF) frameworks, have been used to examine the He:+ ground-state potential curve. The bond lengths of the equilibrium and transition structures have been optimized at all orders of perturbation theory. It is found that RMPn describes the homolytic dissociation bet...

We implement the minimax approximation for the decomposition of energy denominators in Laplace-transformed Moller-Plesset perturbation theories. The best approximation is defined by minimizing the Chebyshev norm of the quadrature error. The application to the Laplace-transformed second order perturbation theory clearly shows that the present method is much more accurate than other numerical qua...

Factorial design and principal component analyses are applied to CH,F infrared frequencies and intensities calculated from ab initio wave functions. In the factorial analysis, the quantitative effects of changing from a 6-31G to a 6-311G basis, of including polarization and diffuse orbitals, and of correcting for electron correlation using the second-order Moller-Plesset procedure are determine...

The infrared (IR) and Raman spectra of triphenylene with intensities were calculated using both density functional theory (DFT, B3LYP method) and Moller-Plesset perturbation method of second order (MP2) with ccpVDZ basis set. Spectra were compared with experimentally measured; the agreement between the observed and calculated spectra is good in case of IR spectroscopy, MP2 simulated spectra wer...

A systematic method for approximating the ab initio electronic energy of molecules from the energies of molecular fragments has been adapted to estimate the total electronic energy of crystal lattices. The fragmentation method can be employed with any ab initio electronic structure method and allows optimization of the crystal structure based on ab initio gradients. The method is demonstrated o...

This Perspective provides an overview of state-of-the-art ab initio quantum chemical methodology and applications. The methods that are discussed include coupled cluster theory, localized second-order Moller-Plesset perturbation theory, multireference perturbation approaches, and density functional theory. The accuracy of each approach for key chemical properties is summarized, and the computat...

We recently developed a scheme to use low-cost calculations find single twist angle where the coupled cluster doubles energy of calculation matches twist-averaged in finite unit cell. used initiator full configuration interaction quantum Monte Carlo as an example exact method beyond theory show that this selected approach had comparable accuracy methods cluster. Furthermore, at least for small ...

We present a method for computing a basis of localized orthonormal orbitals (both occupied and virtual), in whose representation the Fock matrix is extremely diagonal dominant. The existence of these orbitals is shown empirically to be sufficient for achieving highly accurate second-order Moller-Plesset (MP2) energies, calculated according to Kapuy's method. This method (which we abbreviate KMP...

A kink-based path integral method, previously applied to atomic systems, is modified and used to study molecular systems. The method allows the simultaneous evolution of atomic and electronic degrees of freedom. The results for CH4, NH3, and H2O demonstrate this method to be accurate for both geometries and energies. A comparison with density functional theory (DFT) and second-order Moller-Ples...

Using newly developed correlation consistent basis sets for gold, the relative energies for the neutral Au8 geometric isomers have been re-evaluated and the vertical ionization potentials calculated. The results using the correlation consistent basis sets show that second-order Moller-Plesset perturbation theory calculations strongly favor nonplanar Au8 structures for all basis sets that were e...