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.

Theory and mechanism of the allylidenecyclopropane to methylenecyclopentene thermal isomerization

Abstract: The thermally induced rearrangement of 7-(trans-butenylidene)bicyclo[4.1.0]heptane gives 8-methylbicyclo[5.3.0]undeca-1(2),9-diene with stereospecificity that is opposite that predicted by conservation of orbital symmetry. Further, when optically active starting material is thermolyzed, the product is racemic, but recovered starting material is unchanged. Identical results were obtained upon thermolysis of 6-(trans-butenylidene)bicyclo[3.1.0]hexane and of 2-oxo-7-(trans-butenylidene)bicyclo[4.1.0]heptane. These results require that the reaction proceeds through one or more achiral species, that at least one of them is planar, that they never return to starting material, and that there is a stereospecific pathway from the intermediate(s) to product. 6-Electron-6-orbital CASSCF calculations with a 6-31G{sup *} basis set reveal that the lowest energy singlet intermediates on the parent C{sub 6}H{sub 8} energy surface are the achiral cisoid and transoid orthogonal 2-(1`-allyl)allyl biradicals. Besides the cyclopropanes and methylenecyclopentene, the lowest energy species on the entire energy surface is the planar transoid vinyltrimethylenemethane triplet. The orthogonal bisallyl singlets are 8 kcal/mol higher in energy than the planar triplet at this level of theory. 17 refs., 3 figs., 4 tabs.

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

Abstract: The orbital momentum profiles and binding energy spectra for the complete valence shell of propane are reported. The experiment has been performed using a high energy resolution (ΔE=0.95 eV FWHM) multichannel (e,2e) electron momentum spectrosocopy spectrometer at an impact energy of 1200 eV plus the binding energy. The measured binding energy spectra are compared and consistent with PES data available in the literature and also with the predictions of Hartree–Fock, Green’s function and MRSD-CI methods. A strong splitting observed in the inner valence energy spectra due to electron correlation and ion relaxation effects is confirmed by MRSD-CI calculations. The experimental momentum profiles have been compared with calculations obtained using the target Hartree–Fock method with a minimum basis set and also a very large basis set. Density functional theory calculations using B3LYP functionals as well as large basis set MRSD-CI calculations are also reported. The agreement between theory and experiment for t...

Theoretical and electron spin resonance studies of the H⋯H, H⋯D, and D⋯D spin-pair radicals in rare gas matrices: A case of extreme singlet–triplet mixing

Abstract: The H⋯H, H⋯D, and D⋯D spin-pair radicals have been thoroughly investigated in neon, argon, krypton, and xenon matrices near 4 K by electron spin resonance (ESR). A theoretical model has been developed that treats these spin-pairs as weakly interacting atoms. The model includes the effects of 3Σ/1Σ mixing in the analysis of the observed ESR spectral results and yields a consistent set of magnetic parameters for these three isotopomers in all four rare gas hosts. The consideration of H atoms interacting with other H atoms over a distribution of internuclear distances in the rare gas lattice is included in the theoretical and experimental analyses. Application of the model to earlier ESR results for H⋯CH3 reveals a value for its Heisenberg exchange interaction (J) which is found to be considerably larger than that for the H⋯H spin-pair. The effects of methane and neon on the J value are calculated for these spin-pairs. The H⋯H case is unusual in that the nuclear hyperfine interaction (A) is considerably larg...

Ab Initio Investigation of Several Low-lying States of All-trans Octatetraene

Abstract: The results of ab initio calculations that examine vertical and nonvertical transitions to several low-lying states of all-trans-octatetraene are presented. It is found that the lowest vertical excitation is to a valence A-A* 'B, state, and the nominally doubly excited 2 ' 4 state occurs approximately 0.4 eV higher at the geometry of the ground state. Using estimated excited-state equilibrium geometries, we find that the 2 ' 4 state is indeed the lowest singlet excited state, having a (HI transition energy of 4.15 eV. The 0-0 transition energy for the 1 lB, state is calculated to be 4.56 eV. The present results are compared with past theoretical and experimental results.

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.