对含重元素体系的接合二分量-标量相对论密度泛函计算方法

在相对论密度泛函ZORA方法的基础上,提出一种用于含重元素体系的接合二分量-标量相对论密度泛函计算方法.对于只含少数几个重元素的较大体系,仅对其中旋轨耦合作用强的重元素作二分量相对论计算,而对体系的其余部分则作标量相对论计算,通过对动能矩阵元的近似处理实现两种计算的接合.对一系列含6p区重元素分子进行计算的结果表明,当非重元素是第三周期以前的元素时,此方法与二分量ZO-RA方法的计算结果吻合得很好.当非重元素为第四周期元素时,计算结果有一定偏差,表明在后一种情况下旋轨耦合作用已比较显著,但误差仍在目前近似密度泛函计算的精度范围内.此方法可以有效地节省计算量,而且避免了Dyall方法的缺点.     

Automated error control in divide‐and‐conquer self‐consistent field calculations

In linear‐scaling divide‐and‐conquer (DC) electronic structure calculations, a buffer region is used to control the error introduced by the DC approximation. In this study, an energy‐based error estimation scheme is proposed for the DC self‐consistent field method with a two‐layer buffer region scheme. Based on this scheme, a procedure to automatically determine the appropriate buffer region in the DC method is proposed. It was confirmed that the present method works satisfactorily in calculations of water clusters and proteins, although its performance was insufficient for the calculation of a delocalized graphene system. © 2018 Wiley Periodicals, Inc.     

Potential/current characteristics of the ferrous—thionine photogalvanic cell

Experimental potential/current results for a ferrous—thionine photogalvanic cell are compared with calculations based on an earlier proposed mechanistic scheme. There is good agreement. A brief discussion is given of factors influencing the performance of this type of photogalvanic system.     

Towards a spin-adapted coupled-cluster theory for high-spin open-shell states

A spin-adapted coupled-cluster (SA-CC) scheme based on the additional consideration of spin constraints is proposed for the quantum chemical treatment of high-spin open-shell cases. Its computational feasibility is demonstrated via a pilot implementation within the singles and doubles approximation. Test calculations indicate that the suggested SA-CC scheme provides results of similar accuracy as the more traditional schemes without spin adaptation.     

A subsystem density-functional theory approach for the quantum chemical treatment of proteins

We present an extension of the frozen-density embedding (FDE) scheme within density-functional theory [T. A. Wesolowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993)] that can be applied to subsystems connected by covalent bonds, as well as a practical implementation of such an extended FDE scheme. We show how the proposed scheme can be employed for quantum chemical calculations of proteins by treating each constituting amino acid as a separate subsystem. To assess the accuracy of the extended FDE scheme, we present calculations for several dipeptides and for the protein ubiquitin.     

Application of the additive interatomic interaction model to the theoretical analysis of molecular vibrations: Analysis of the normal vibrations of CH3NO2, CH3NHNO2 and their deutero-derivatives

A model is proposed based on the additivity of interatomic interactions for describing molecular vibrational spectra. The parameters which are introduced and the possibilities of simplification in a scheme of calculations are discussed. The model is applied to the calculation and analysis of normal vibrations of nitromethane, N-methylnitroamine and their deutero-derivatives.     

A numerical integration scheme for the evaluation of correlation energy functionals

A numerical integration scheme is presented for three-dimensional integrals occurring in electronic structure calculations, concentrating attention on the evaluation of the correlation energy through a density-functional expression. The scheme is based on the choice of density-based weight functions that naturally partition the space into “atomic” volumes (in which the integration is performed in terms of spherical coordinates) and “diatomic” volumes (in which the integration is performed in terms of confocal elliptical coordinates). Such a choice is justified on the basis of the analytical behavior of the integrand. The attainable accuracy and the required computational effort within the proposed scheme are discussed in detail in a test application on the C₆₀ molecule in the symmetrical configuration. Finally, a comparison with previously proposed schemes is presented. © 1993 John Wiley & Sons, Inc.     

A scheme for rapid prediction of cooperativity in hydrogen bond chains of formamides,acetamides, and N‐methylformamides

A scheme is proposed in this article to predict the cooperativity in hydrogen bond chains of formamides, acetamides, and N‐methylformamides. The parameters needed in the scheme are derived from fitting to the hydrogen bonding energies of MP2/6‐31+G** with basis set superposition error (BSSE) correction of the hydrogen bond chains of formamides containing from two to eight monomeric units. The scheme is then used to calculate the individual hydrogen bonding energies in the chains of formamides containing 9 and 12 monomeric units, in the chains of acetamides containing from two to seven monomeric units, in the chains of N‐methylformamides containing from two to seven monomeric units. The calculation results show that the cooperativity predicted by the scheme proposed in this paper is in good agreement with those obtained from MP2/6‐31+G** calculations by including the BSSE correction, demonstrating that the scheme proposed in this article is reasonable. Based on our scheme, a cooperativity effect of almost 240% of the dimer hydrogen bonding energy in long hydrogen bond formamide chains, a cooperativity effect of almost 190% of the dimer hydrogen bonding energy in long hydrogen bond acetamide chains, and a cooperativity effect of almost 210% of the dimer hydrogen bonding energy in long hydrogen bond N‐methylformamide chains are predicted. The scheme is further applied to some heterogeneous chains containing formamide, acetamide, and N‐methylformamide. The individual hydrogen bonding energies in these heterogeneous chains predicted by our scheme are also in good agreement with those obtained from Møller‐Plesset calculations including BSSE correction. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Diels-Alder addition of some 6-and 5-member ring aromatic compounds on the Si(001)-2×1 surface: dependence of the binding energy on the resonance energy of the aromatic compounds

An energy decomposition scheme is proposed for understanding of the relative low binding energy of the [4+2] cycloaddition of benzene on the Si(001)-2×1 surface. By means of density functional cluster model calculations, this scheme is demonstrated to be applicable to some other 6- and 5-member ring aromatic compounds, giving a trend that the binding energy of the [4+2] cycloaddition products of those aromatic compounds on the Si(001) surface depends strongly on their resonance energy.     

A technique for orbital exponent optimization in ab initio HF?SCF?LCAO?MO calculations

A technique for Slater orbital exponent optimization in an HF? SCF? LCAO? MO calculation is proposed in which orbital exponent variation is incorporated into the SCF scheme. This is accomplished by rewriting Slater's rules so that the shielding terms depend on the molecular charge distribution through the elements of the population matrix. The SCF scheme then includes a calculation of a new set of orbital exponents from the coefficients of self-consistent molecular orbitals obtained from the previous set of exponents. The process is iterated until the energy attains its lowest value. The technique is illustrated by minimal basis calculations on LiH, BH, and HF. Near optimization is obtained with considerably less effort than is necessary for other reported techniques. Aside from interesting properties, the technique can be important for extended basis calculations where exponent optimization is a difficult task.     

Mechanism of phenol degradation processes induced by direct-current atmospheric-pressure discharge in air

The phenol degradation kinetics and the buildup kinetics of the products hydroxyphenols, nitrophenols, carboxylic acids, and formaldehyde in electrolytic-cathode direct-current discharge have been studied, as well as the formation of nitric acid. On the basis of the results, a scheme of the processes has been proposed; calculations according to this scheme describe well the experimental data on the degradation kinetics of phenol and the formation/decay kinetics of its transformation products.     

Optimization of calculations for the preparation of standard solutions

The calculations necessary in the preparation of a large number of solutions used as standards, are time-consuming and tedious. The scheme proposed significantly shortens the time and makes the work more routine. The equations used are derived from wellknown stoichiometric expressions and mathematical representations of some necessary restrictions. The scheme has advantages when many solutions must be prepared for any analytical method.     

Rotational-vibrational symmetry correlations in molecular collisions: The A3(C2v + A → A2 + A2 system

A rotational-vibrational correlation scheme based on the conservation of permutation-inversion symmetries is proposed, which makes no assumptions on the collision geometry. The possible use of these symmetries in state-to-state calculations to avoid similar assumptions is stressed. The scheme is applied to the reaction A₃(C_2v) + A → A₂ + A₂.     

Diels-Alder addition of some 6- and 5-member ring aromatic compounds on the Si(001)-2×l surface: dependence of the binding energy on the resonance energy of the aromatic compounds

An energy decomposition scheme is proposed for understanding of the relative low binding energy of the [4+2] cycloaddition of benzene on the Si(001)-2x1 surface. By means of density functional cluster model calculations, this scheme is demonstrated to be applicable to some other 6- and 5-member ring aromatic compounds, giving a trend that the binding energy of the [4+2] cycloaddition products of those aromatic compounds on the Si(001) surface depends strongly on their resonance energy.     

Nonorthogonal ultralocalized functions and fitted Wannier functions for local electron correlation methods for solids

Despite the formal exponential decay behavior of Wannier functions (WFs), their spatial extent, which is a key parameter determining the computational cost of local correlation calculations for solids, is still rather large. The problems with the localization of the WFs can partly be attributed to their mutual orthogonality. Possibilities of reduction of the spatial extent of the WFs without losing the accuracy of the calculations are investigated. A method for generation of nonorthogonal ultralocalized functions based on maximization of their Löwdin populations is developed. A scheme for fitting of the WFs and nonorthogonal localized functions with a limited support is proposed. The calculations show that by combining both techniques one can obtain quite compact linearly independent localized functions, which may significantly decrease the computational cost in post-HF calculations.     

Double even tempering of orbital exponents: Application to Roothaan-Hartree-Fock calculations for He through Xe in Slater-type basis sets

Summary Double even tempering (DET) of orbital exponents is proposed as a useful generalization of even tempering (ET). The DET scheme uses two sets of basis functions for each angular momentum. The two sets have different principal quantum numbers and their exponents are generated by two different geometric sequences. Roothaan-Hartree-Fock (RHF) calculations on the atoms from He through Xe using both ET and DET Slater-type basis sets of the same size are carried out to demonstrate the substantial improvement offered by the DET scheme. The DET scheme reduces the maximum deviation of the RHF energies relative to the Hartree-Fock limit from 1.4 to 0.3 millihartrees.     

Enhancing the accuracy of virtual screening: molecular dynamics with quantum-refined force fields

Summary A methodology aimed at improving the accuracy of current docking–scoring procedures is proposed, and validated through detailed tests of its performance in predicting the activity of HIV-1 protease inhibitors. This methodology is based on molecular dynamics simulations using a force field whose effective charges are refined by means of a novel procedure that relies on quantum-mechanical calculations and preserves the internal consistency of the parameterization scheme.     

Comparison study of several numerical integration schemes used in calculations of density functional theory

Several numerical integration schemes for the evaluation of matrix elements in density functional theory calculations have been studied and compared by computational practice. The best scheme was found to be the combination of the atomic partition function proposed by Becke with the scaled generalized Gauss-Laguerre quadrature formula for radial integration suggested by Yang, which achieve the highest convergence rate to the numerical integration. With the same number of integration points, the accuracy of the calculated results by this scheme is higher by 1 to 2 orders of magnitudes than that by other schemes. The reason for achieving higher accuracy by this scheme has been proposed preliminarily.     

分子间相互作用的研究——-价轨道模型势从头算能量分解法

研究分子间相互作用是了解液体,固体性质和结构以及气体性质的关键,也是研究化学和生物化学催化机制及化学反应途径的重要方面.因此,近几年来这个领域的理论和实验研究引起了人们广泛的兴趣并取得了长足的进步.特别值得指出的是Morokuma等提出的基于单行列式从头算的能量分解法,较好地解决了很多体系中分子间相互作用的本质问题,受到了理论化学界的普遍重视.但是这种方法很费计算机时间,对于较大的体系,特别是含有重原子的体系,应用受到了限制.因此简化这种方法,使它能够比较容