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.

Rotationally resolved laser photoelectron spectra of gas-phase NO: rotational propensity rules in photoionization

Abstract: Rotationally resolved laser photoelectron spectra were recorded by exciting specific rovibronic levels in the A/sup 2/..sigma../sup +/, C/sup 2/II, and D/sup 2/..sigma../sup +/ Rydberg states of NO, to study the rotational propensity rules in photoionization. The data for the A and C states are in excellent agreement with theoretical calculations of Bonham et al. and the model of Pratt et al. The D state spectra show, in addition to the expected propensities, a strong ..delta..N = 0 peak. On the basis of theoretical calculations they infer that the continuum wave excited by ionizing NO from its D state cannot be adequately described by a single l quantum number.

Evaluation of a characteristic atomic radius by an ab initio method

Abstract: The MELD program is employed to evaluate the Slater average potential v(r) felt by an electron at the point r within an atom. The characteristic radius R of the atom is then defined by the classical turning point equation v(R) = −I, where I denotes the first ionization potential of the atom. The atomic radii defined in this way have a close correlation with the van der Waals atomic radii. © 1997 John Wiley & Sons, Inc.

Population analyses that utilize projection operators

Abstract: Several different methods have been explored that partition the 3-D space of a molecule into its atomic components using Hermitian one-electron position-space projection operators, PA. Previously, we defined PA so that hard interatomic boundaries between atoms are observed. This idea has been extended to allow softer boundaries that have a region of overlap between atoms that can be controlled through an iterative process. Functions that determine the shape of the atomic volume are also discussed. The atomic electron populations of 17 different systems are presented as a function of these two factors. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 384–394, 2003

Singlet-Triplet Energy Separations in Some Hydrocarbon Diradicals

Abstract: A diradical is literally a molecule with two unpaired electrons. We prefer the somewhat broader definition of a diradical as a molecule in which two electrons occupy a degenerate or nearly degenerate pair of orbitals. Group theory predicts a symmetry enforced degeneracy for a pair of orbitals, occupied by a total of two electrons, in the most symmetrical molecular geometry of methylene (CH2), cydobutadiene (CBD), and trimethylenemethane (TMM) (see Figure 1). Thus, we consider all three of these molecules to be diradicals. CH2 is the simplest molecule containing a divalent carbon atom. Although a very large number of other carbenes have been �!udied (1-3), in this review we confine our discussion to the parent hydro­ carbon. CBD yields to cyclopropenyl anion (4, 5) the position of being the smallest fully conjugated cyclic hydrocarbon containing 4n pi elec­ trons; but the former annulene has received more attention. Therefore, our discussion of molecules that are diradicals by virtue of being antiaromatic annulenes focuses on CBD. We have also chosen to discuss another four pi electron system, TMM, as representative of the class of diradicals that are fully conjugated hydrocarbons but for which no classical Kekule structures can be written (6). TMM is the simplest such molecule and, again, the best studied.

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.