Electron propagator theory methods

Hartree-Fock (HF), molecular orbital theory satisfies most of the criteria, but qualitative failures and quantitative discrepancies with experiment often render it useless. Methods that systematically account for electron correlation, employed in pursuit of more accurate predictions, often lack a consistent, interpretive apparatus. Among these methods, electron propagator theory [1] is distinguished by its retention of many conceptual advantages that facilitate interpretation of molecular structure and spectra [2, 3, 4, 5, 6, 7, 8, 9]. 

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. 

It is also possible to employ highly correlated reference states as an alternative to methods that employ Hartree-Fock orbitals. Multiconfigu-rational, spin-tensor, electron propagator theory adopts multiconfigura-tional, self-consistent-field reference states [37], Perturbative corrections to these reference states have been introduced recently [38],... 

In this book, the experts who have developed and tested many of the currently used electronic structure procedures present an authoritative overview of the theoretical tools for the computation of thermochemical properties of atoms and molecules. The first two chapters describe the highly accurate, computationally expensive approaches that combine high-level calculations with sophisticated extrapolation schemes. In chapters 3 and 4, the widely used G3 and CBS families of composite methods are discussed. The applications of the electron propagator theory to the estimation of energy changes that accompany electron detachment and attachment processes follow in chapter 5. The next two sections of the book focus on practical applications of the aforedescribed... 

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]. 

For such nonequilibrium processes, the direct mapping of the electron propagator methods to calculations of electric current becomes inapplicable because of the time-dependent nature of electric current in both phenomena. A time-dependent problem requires the further development of the theory of Green s functions to electron dynamics in which e-e correlation effects are taken into account. Such methodology already exists in physics in which many-body ideas have been developed for time-dependent problems. This theory is based on nonequilibrium Green s or Keldysh functions [2,5, 6, 40-46]. 

William Lipscomb s career forever will be identified with the theory of the three-center bond in boron hydrides. His celebrated work in this field employed an incisive mixture of experimental and theoretical methods. In his laboratory, developers of conceptual and computational tools were given ample scope, for the Colonel has a knack for connecting new theoretical capabilities to significant chemical questions. We therefore offer this work, an application of the electron propagator picture of electronic structure, in tribute to his skills as a mentor of young scientists. 

One possible way to treat such a case is to use an approximated approach of the nonadiabatic electron wavepacket theory, the phase-space averaging and natural branching (PSANB) method [493], or the branching-path representation, in which the wavepackets propagate along non-Born-Oppenheimer branching paths. 

For the second approach, called Car-Parrinello (CP) direct dynamics, the electronic wavefunction and nuclear motion are propagated simultaneously. When applying this method within the framework of density functional theory (DFT), the wavefunction is propagated by using fictitious electronic degrees of freedom with arbitrary masses. In ab initio and semiem-pirical electronic structure theories, the wavefunction is expanded in a set of basis functions and then as a superposition of zeroth-order electronic state... 

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