Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set

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.

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

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.

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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

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。

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

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.

General atomic and molecular electronic structure system

Theoretical spherically averaged momentum distributions for canonical Hartree-Fock and Dyson orbitals are presented for methylamine and compared with the EMS spectra. Theoretical spin densities are also reported for the radical cation and compared with the EPR spectrum. To the first approximation, both of these experiments give information about the HOMO of neutral molecule. Both results clearly show effects from hyperconjugative delocalmization of the nitrogen lone-pair onto the methyl group

Momentum distributions, spin distributions, and bonding in methylamine and its radical cation

The particle–particle random phase approximation (pp-RPA) for calculating excitation energies has been applied to diradical systems. With pp-RPA, the two nonbonding electrons are treated in a subspace configuration interaction fashion while the remaining part is described by density functional theory (DFT). The vertical or adiabatic singlet–triplet energy gaps for a variety of categories of diradicals, including diatomic diradicals, carbene-like diradicals, disjoint diradicals, four-π-electron diradicals, and benzynes are calculated. Except for some excitations in four-π-electron diradicals, where four-electron correlation may play an important role, the singlet–triplet gaps are generally well predicted by pp-RPA. With a relatively low O(r4) scaling, the pp-RPA with DFT references outperforms spin-flip configuration interaction singles. It is similar to or better than the (variational) fractional-spin method. For small diradicals such as diatomic and carbene-like ones, the error of pp-RPA is slightly larg...

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Singlet--Triplet Energy Gaps for Diradicals from Particle--Particle Random Phase Approximation

Complete pi‐space CI calculations have been performed for the 1E′ state of trimethylenemethane in a planar D3h conformation using an STO‐3G basis. Molecular orbitals were defined by SCF calculations with C2v symmetry constraints for the lowest 3B2 and 1B2 states. As expected, the 3B2 orbitals had nearly D3h symmetry while the 1B2 pi orbitals were severely distorted. Full pi‐space configuration interaction calculations for both components of the 1E′ state using each set of molecular orbitals gave four nearly identical energies. This verified that the sigma cores from the two SCF calculations were essentially identical. The 1B2 component of the 1E′ wavefunction resembles an allyl radical plus an electron in a p orbital localized on one methylene group. Hence rotation of this methylene group into a plane orthogonal to the allyl radical should produce only a small change in energy.

Configuration interaction calculations for 1E′ trimethylenemethane

The 13 electron BeF radical has been generated and trapped in argon and krypton matrices at 12 K and studied via ESR spectroscopy. Comparisons are made between BeF and other similar radicals. The calculated dipole moment for BeF is 1.1 D. The magnetic parameters in argon are g∥=2.001, g⊥=2.001, Aiso(Be)=294(2) MHz, and Aiso(19F) =230(2) MHz. The 19F hfs is unusually isotropic for an MF radical, suggesting that rotational averaging might be occurring. Results of ab initio theoretical calculations are compared to the observed A tensors. The BeF molecule was generated by the codeposition of thermally produced Be atoms and molecular fluorine in the rare gas matrices.

The generation and ESR investigation of the BeF radical in rare gas matrices

ZEKE spectra of propylaniline were recorded by exciting 13 vibronic levels in the S1 electronic state. All ZEKE spectra show well resolved vibrational structure of the anti and gauche cations. Adiabatic ionization potentials of the anti and gauche conformations were determined to be 59 717±3 cm−1 (7.4040 eV) and 59 793±3 cm−1 (7.4134 eV), respectively. A number of ring modes as well as several low‐frequency torsional and bending chain modes have been identified. Spectra demonstrate that low‐frequency chain modes are sensitive to the molecular conformation. Ab initio calculations were performed to understand the nature of these low‐frequency chain modes. S1←S0 vibronic transitions involving anti and gauche conformations can easily be distinguished using the ZEKE method.

Ernest R. Davidson

Papers

Momentum distributions, spin distributions, and bonding in methylamine and its radical cation

Singlet--Triplet Energy Gaps for Diradicals from Particle--Particle Random Phase Approximation

Configuration interaction calculations for 1E′ trimethylenemethane

The generation and ESR investigation of the BeF radical in rare gas matrices

High‐resolution zero kinetic energy photoelectron spectra of para‐n‐propylaniline