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

The low‐lying electronic states of the Be2 molecule have been examined using MO SCF CI with a basis set of elliptical orbitals. The ground state of the molecule was found to be repulsive in the best calculation. The excited states all seem to be bound with potential curves similar to that predicted for Be2+. Two new techniques for improving the convergence of configuration interaction are introduced and applied to the ground‐state calculation.

Theoretical Calculation of the Potential Curves of the Be2 Molecule

The 1(π,π*) state of ethylene has been thoroughly investigated at the configuration interaction level utilizing an extensive basis set and a configuration selection scheme which emphasizes a correct description of all correlation effects involving the π or π* electrons. The result, contrary to the Hartree–Fock prediction, but in agreement with the general experimental conclusion, is a mostly valence state as indicated by a value for 〈π*‖x2‖π*〉 of 8.8 a.u. using the π* natural orbital. A calculated excitation energy of 7.96 eV is in reasonable agreement with the 7.65 eV experimental absorption maximum. It is found that σ→σ* excitations relative to the ground state are essential to describe the left–right correlation of σ electrons with the π* electron. This in turn compensates for the ionic πA 2–πB 2 nature of the 1(π,π*) state, allowing the SCF state to become contracted at the CI level. The π* orbital in the second 1(π,π*) state appears to be well characterized at a CI level as a 3d orbital constrained t...

Configuration interaction calculations on the planar 1(π,π*) state of ethylene

The transition metal-carbonyl bond

Extended x-ray-absorption fine-structure amplitudes-Wave-function relaxation and chemical effects

The fundamental goal of quantum chemistry is the development of a qualitatively correct set of concepts for describing the chemical and physical properties of molecules. When this goal is achieved, a well-trained chemist should be able to correlate and predict the behavior of most chemical systems without extensive calculation. In order to achieve this goal it is necessary to obtain high-accuracy wave functions for a few typical chemical systems. Further it is necessary to understand these wave functions on two levels. First one must understand what types of terms and effects must be included in the mathematical description of the wave function. This level of understanding has probably now been attained as a result of twenty years of large-scale calculations. On the second level one must understand the relationship between the physical and chemical properties of the constituent parts of the system and the physical and chemical properties exhibited by the system itself. This level of understanding has proven frustratingly difficult to achieve by the direct ab-initio approach.

Ernest R. Davidson

Papers

Theoretical Calculation of the Potential Curves of the Be2 Molecule

Configuration interaction calculations on the planar 1(π,π*) state of ethylene

The transition metal-carbonyl bond

Extended x-ray-absorption fine-structure amplitudes-Wave-function relaxation and chemical effects

Configuration interaction description of electron correlation