Ernest R. Davidson

Bio: Ernest R. Davidson is an academic researcher from University of Washington. The author has contributed to research in topics: Configuration interaction & Ab initio. The author has an hindex of 78, co-authored 480 publications receiving 30616 citations. Previous affiliations of Ernest R. Davidson include Lawrence Livermore National Laboratory & Indiana University.

Orbital momentum profiles and binding energy spectra for the complete valence shell of molecular fluorine

Abstract: The first electronic structural study of the complete valence shell binding energy spectrum of molecular fluorine, encompassing both the outer and inner valence regions, is reported. These binding energy spectra as well as the individual orbital momentum profiles have been measured using an energy dispersive multichannel electron momentum spectrometer at a total energy of 1500 eV, with an energy resolution of 1.5 eV and a momentum resolution of 0.1 a.u. The measured binding energy spectra in the energy range of 14–60 eV are compared with the results of ADC(4) many-body Green's function and also direct-CI and MRSD-CI calculations. The experimental orbital electron momentum profiles are compared with SCF theoretical profiles calculated using the target Hartree-Fock approximation with a range of basis sets and with Density Functional Theory predictions in the target Kohn-Sham approximation with non-local potentials. The truncated (aug-cc-pv5z) Dunning basis sets were used for the Density Functional Theory calculations which also include some treatment of correlation via the exchange and correlation potentials. Comparisons are also made with the full ion-neutral overlap amplitude calculated with MRSD-CI wavefunctions. Large, saturated basis sets (199-GTO) were employed for both the high level SCF near Hartree-Fock limit and MRSD-CI calculations to investigate the effects of electron correlation and relaxation.

Matrix elements for spin‐adapted configurations

Abstract: It is shown that the turn-over rule which is used to simplify matrix elements between spin-projected Slater determinants may also be used to simplify formation of matrix elements between any orthonormal set of spin-coupled Slater determinants. The coefficients for the spin-coupling may then be chosen freely to reduce the number of important configurations in the secular equation.

Theoretical study of hydridocobalt carbonyls

Abstract: The molecular geometry and electronic structure of hydridocobalt tri- and tetracarbonyls were investigated, by means of ab initio Hartree-Fock calculations in a Gaussian basis set. Two conformations of the tetracarbonyl were found, both having the d/sup 8/, closed-shell electronic configuration. The tricarbonyl complex was found to possess a number of conformations, as well as several low-energy electronic configurations. They examine the geometry, frontier orbitals, and character of chemical bonds of these forms of HCo(CO)/sub 4/ and HCo(CO)/sub 3/, with the aim of determining their relevance to the catalytic activity of the compounds.

Two new hexanuclear iron(III) complexes with S = 5 ground states

Abstract: The synthesis and magnetic properties of two new hexanuclear iron complexes [Fe6O2(OH)2(O2CR)10L2] (R = But (3), Me (4); LH = 2-(2-hydroxyethyl)pyridine (hepH) (3), 6-methyl-2-(hydroxymethyl)pyridine (Me-hmpH) (4)) are reported. Both compounds are prepared by treatment of [Fe3O(O2CR)6(H2O)3]+ with three equivalents of LH in MeCN. The X-ray crystal structure of 3·2CHCl3·2H2O is presented. It consists of a planar array of six Fe3+ ions comprising two [Fe3(μ3-O)] subunits that are related by an inversion centre and linked at two of their apices, each linkage consisting of one μ-hydroxo and two μ-carboxylato groups. DC magnetic susceptibility measurements at 1.0 and 0.10 Tesla in the 2.0–300 K range show an increase in the effective magnetic moment with decreasing temperature, corresponding to a high spin (S) ground state. The spin of the ground state was established by magnetization measurements in the 1.0–7.0 T field range and 1.7–4.0 K temperature range. Fitting of the reduced magnetization data by full matrix diagonalization, incorporating both axial and rhombic anisotropy, gave S = 5, g = 1.96, D = 0.46 cm−1 and |E| = 0.046 cm−1 for 3, and S = 5, g = 2.07, D = 0.27 cm−1 and |E| = 0 cm−1 for 4. Alternative fits with a negative ZFS were rejected based on their relative fitting error as well as on measurements of the magnetization relaxation behaviour of the complexes at very low temperature (≥0.04 K), where no hysteresis characteristic of a single-molecule magnet was observed.

Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen

Abstract: In the past, basis sets for use in correlated molecular calculations have largely been taken from single configuration calculations. Recently, Almlof, Taylor, and co‐workers have found that basis sets of natural orbitals derived from correlated atomic calculations (ANOs) provide an excellent description of molecular correlation effects. We report here a careful study of correlation effects in the oxygen atom, establishing that compact sets of primitive Gaussian functions effectively and efficiently describe correlation effects i f the exponents of the functions are optimized in atomic correlated calculations, although the primitive (s p) functions for describing correlation effects can be taken from atomic Hartree–Fock calculations i f the appropriate primitive set is used. Test calculations on oxygen‐containing molecules indicate that these primitive basis sets describe molecular correlation effects as well as the ANO sets of Almlof and Taylor. Guided by the calculations on oxygen, basis sets for use in correlated atomic and molecular calculations were developed for all of the first row atoms from boron through neon and for hydrogen. As in the oxygen atom calculations, it was found that the incremental energy lowerings due to the addition of correlating functions fall into distinct groups. This leads to the concept of c o r r e l a t i o n c o n s i s t e n t b a s i s s e t s, i.e., sets which include all functions in a given group as well as all functions in any higher groups. Correlation consistent sets are given for all of the atoms considered. The most accurate sets determined in this way, [5s4p3d2f1g], consistently yield 99% of the correlation energy obtained with the corresponding ANO sets, even though the latter contains 50% more primitive functions and twice as many primitive polarization functions. It is estimated that this set yields 94%–97% of the total (HF+1+2) correlation energy for the atoms neon through boron.

The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals

Abstract: We present two new hybrid meta exchange- correlation functionals, called M06 and M06-2X. The M06 functional is parametrized including both transition metals and nonmetals, whereas the M06-2X functional is a high-nonlocality functional with double the amount of nonlocal exchange (2X), and it is parametrized only for nonmetals.The functionals, along with the previously published M06-L local functional and the M06-HF full-Hartree–Fock functionals, constitute the M06 suite of complementary functionals. We assess these four functionals by comparing their performance to that of 12 other functionals and Hartree–Fock theory for 403 energetic data in 29 diverse databases, including ten databases for thermochemistry, four databases for kinetics, eight databases for noncovalent interactions, three databases for transition metal bonding, one database for metal atom excitation energies, and three databases for molecular excitation energies. We also illustrate the performance of these 17 methods for three databases containing 40 bond lengths and for databases containing 38 vibrational frequencies and 15 vibrational zero point energies. We recommend the M06-2X functional for applications involving main-group thermochemistry, kinetics, noncovalent interactions, and electronic excitation energies to valence and Rydberg states. We recommend the M06 functional for application in organometallic and inorganometallic chemistry and for noncovalent interactions.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

General atomic and molecular electronic structure system

Abstract: A description of the ab initio quantum chemistry package GAMESS is presented. Chemical systems containing atoms through radon can be treated with wave functions ranging from the simplest closed-shell case up to a general MCSCF case, permitting calculations at the necessary level of sophistication. Emphasis is given to novel features of the program. The parallelization strategy used in the RHF, ROHF, UHF, and GVB sections of the program is described, and detailed speecup results are given. Parallel calculations can be run on ordinary workstations as well as dedicated parallel machines. © John Wiley & Sons, Inc.