Ab initio electron propagator methods

Ab Initio Electron Propagator Methods Applications to Fullerenes and Nucleic Acid Fragments... 

V. G. Zakrezewski, O. Dolgounitcheva, A. V. Zakjevskii, and J. V. Ortiz, Annu. Rep. Comput. Chem., 6, 79-94 (2010). Ab Initio Electron Propagator Methods Applications to Fullerenes and Nucleic Acid Fragments. 

Net atomic charges of about -0.2 at each H were calculated with an ab initio MO-SCF method [2], with the semiempirical CNDO/2 method [11], and with another semiempirical method using localized bond orbitals for Cl [12]. A lower value came from an EH calculation [3]. A radial electron density distribution was calculated within the united-atom approximation [10]. Two different dipole moments were obtained with an MO-SCF calculation (yielding also quadrupole and octupole moments) [2] and with the electron propagator theory (EPT) [13]. 

Ab initio molecular dynamics methods can roughly be divided into two classifications Born-Oppenheimer Molecular Dynamics and Car-Parrinello Molecular Dynamics . In both simulations, the wavefunction is propagated with the changes in the nuclear coordinates. In the Born-Oppenheimer MD approach, the forces on each of ions are explicitly calculated at each MD time step. As such, the system directly follows the Bom-Oppenheimer surface. The primary drawback of the Born-Oppenheimer MD approach relates to the fact that time-intensive electronic structure calculations must be converged... 

Electron propagator theory generates a one-electron picture of electronic structure that includes electron correlation. One-electron energies may be obtained reliably for closed-shell molecules with the P3 method and more complex correlation effects can be treated with renormalized reference states and orbitals. To each electron binding energy, there corresponds a Dyson orbital that is a correlated generalization of a canonical molecular orbital. Electron propagator theory enables interpretation of precise ab initio calculations in terms of one-electron concepts. 

Electronic descriptors were calculated for the ab initio optimized (RHG/STO-3G) structures. In addition, logP as a measure of hydrophobicity and different topological indices were also calculated as additional descriptors. A nonlinear model was constructed using ANN with back propagation. Genetic algorithm (GA) was used as a feature selection method. The best ANN model was utilized to predict the log BB of 23 external molecules. The RMSE of the test set was only... 

Early semiempirical calculations laid the foundations for subsequent ab initio methods which can now not only describe the electronic structure of optically accessible excited states, but also model the wavepacket propagation on the resulting potential energy surfaces. These models are supported by ultrafast studies using femptosecond (fs) pulsed lasers with a variety of detection systems. Many systems use indirect detection of excited-state processes because many excited states are unbound and not amenable to spectroscopic techniques. 

The ab initio atom-centered density matrix propagation (ADMP) and the quantum wavepacket ab initio molecular dynamics (QWAIMD) computational methods are briefly described. Studies on vibrational and electronic properties obtained utilizing these methods are highlighted. 

Table III gives a complication of the ab initio molecular polarization propagator calculations that have appeared since the previous survey of the literature up through 1977 (Oddershede, 1978). Only calculations which go beyond RPA are included in Table III, and to get the full picture of the activity within the field of polarization propagator calculations Table III must be seen in conjunction with Table I. If we compare with Table A.I. of Oddershede (1978) and consider only calculations of the same kind, i.e. exclude atomic calculations and calculations using the CHF method from the previous review, it is evident that the number of polarization propagator calculations, like other kinds of electronic structure calculations, have increased substantially within the last decade and by now is becoming a useful tool in computational quantum chemistry.

In this substection we will shortly discuss the computational methods used for calculation of the spin-spin coupling constants. Two main approaches available are ab initio theory from Hartree-Fock (or self-consistent field SCF) technique to its correlated extensions, and density function theory (DFT), where the electron density, instead of the wave function, is the fundamental quantity. The discussion here is limited to the methods actually used for calculation of the intermolecular spin-spin coupling constants, i. e. multiconfigurational self consistent field (MCSCF) theory, coupled cluster (CC) theory and density functional theory (DFT). For example, the second order polarization propagator method (SOPPA) approach is not... 

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