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.

The Cope Rearrangement Revisited with Multireference Perturbation Theory

Abstract: Earlier calculations on the Cope rearrangement based on a CASSCF wave function for the six electrons in the rearranging bonds gave reasonable energies at most places on the potential surface except in the crucial region around the chair transition state. Recently developed MP2 methods for multireference wave functions yield greatly improved energies. Using our version of this method, we simultaneously find that the CASSCF wave function overestimates the diradical character of the wave function. When this error is corrected, the Dewar-type diradicaloid stable intermediate no longer occurs as a minimum in the potential surface and the aromatic transition state moves to shorter bond lengths.

First Excited 1Σg+ State of the Hydrogen Molecule

Abstract: A variation calculation on the first excited 1Σg+ state of H2 has been carried out using an expansion in elliptical coordinates. All results are reported in Hartree atomic units.The potential function resulting from this calculation is characterized by having minima at R=1.9 and R=4.3 and a maximum at R=3.3.The energy obtained at R=1.9 using a 20‐term, open‐shell, covalent‐type wave function was —0.7162 as compared with the ``experimental'' value of —0.7181. Due to convergence difficulties, many more configurations are required to improve this result significantly. At R=4.3, on the other hand, the best result was obtained with an open‐shell wave function including nine ionic terms and nine atomic terms. This result of —0.7007 is below the reported ``experimental'' value of —0.6935 because the two lowest (2pσ)21Σg+ vibrational levels have not been found experimentally. The energy at the top of the barrier was computed to be —0.6844 and probably is as low as —0.6884.The vibrational levels for this potential...

A theoretical study on the potential surfaces of the lower electronic states of HCO

Abstract: The results of ab initio potential‐energy surface calculations are presented for the lowest four doublet states of HCO. A conical Jahn–Teller intersection was found between the lowest two 2A′ surfaces. The equilibrium geometries of the lowest two quartet states were also calculated. Discussion is primarily focused on the assignment of the hydrocarbon flame bands. The A bands of the hydrocarbon flame bands are assigned as a ?2A′→?2A′ transition which concurs with Dixon’s speculation. As for the ? state which is the origin of the B bands, the most probable state is the bent second 2A″ state which is described by the configuration (6a′)2(7a′)2(1a″)1.

Single‐Configuration Calculations on Excited States of Helium. II

Abstract: The best one‐configuration wavefunctions for several excited states of helium have been found. The error in the energy obtained varies from 0.5% to 1.0% of the binding energy of the outer electron. The method used is shown to give a rigorous upper bound to the excited‐state energy.

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.