Ab initio electron propagator theory

Yu. Dahnovsky, V.G. Zakrzewski, A. Kletsov, J.V. Ortiz, Ab Initio electron propagator theory of molecular wires I. Formalism, J. Chem. Phys. 123 (2005) 184711. 

The spectra of anionic mononucleotides (dXMP, where X = A, C, G, and T) [74] were rather poorly resolved for the first VDEs of dAMP , dCMP, and dTMP , whereas an error bar of 0.10 eV was determined for the VDE of dGMP . Theoretical VDE values obtained in the same paper as B3LYP energy differences between anionic and neutral states were about 0.5-0.8 eV off the experimental peak positions for dTMP, dCMP , and dAMP . No interpretation of other possible transitions was given. Excellent agreement with experimental energy values was achieved for VDEs of mononucleotide anions calculated with ab initio electron propagator theory [71, 75]. 

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. 

Electron propagator theory (EPT) yielded a vertical value of 1.160 eV [28] (see also [29 to 31 ]), MP2 theory gave 1.162 eV (zero point correction included) [32], MP4 theory (using isogyric comparisons with the H2 molecule) 1.23 eV [33], and MP4 + quadratic Cl calculations 1.20 eV [14]. Compare also a 1985-review on theoretical calculations of A [34]. HF calculations on PH2 yielded Koopmans Theorem (KT) electron detachment energies, which depend strongly on the basis sets used [35]. Older ab initio MO-SCF calculations gave unsatisfactory results [17]. 

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]. 

It was shown by Car and Parrinello that classical MD (CPMD, Car-Parrinello molecular dynamics) can be performed in the framework of ab initio electronic theory. In CPMD, coefficients of the electronic basis functions (q ) are treated as dynamical variables with associate mass (//). The trajectories of these fictitious particles representing the electronic wave function ) of the system can propagate simultaneously with the dynamics... 

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... 

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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