Free-energy analysis of the electron-density fluctuation in the quantum-mechanical/molecular-mechanical simulation combined with the theory of energy representation

The relationship is investigated for QM/MM (quantum-mechanical/molecular-mechanical) systems between the fluctuations of the electronic state of the QM subsystem and of the solvation effect due to the QM-MM interaction. The free-energy change due to the electron-density fluctuation around its average is highlighted, and is evaluated through an approximate functional formulated in terms of distribution functions of the many-body coupling (pairwise non-additive) part of the QM-MM interaction energy. A set of QM/MM simulations are conducted in MM water solvent for QM water solute in ambient and supercritical conditions and for QM glycine solute in the neutral and zwitterionic forms. The variation of the electronic distortion energy of the QM solute in the course of QM/MM simulation is then shown to be compensated by the corresponding variation of the free energy of solvation. The solvation free energy conditioned by the electronic distortion energy is further analyzed with its components. It is found that the many-body contribution is essentially equal between the free energy and the average sum of solute-solvent interaction energy.     

Accurate calculation of the binding energy of the water dimer

The binding energy of the water dimer is calculated at the MP2 level using efficient basis sets augmented with bond functions. The intermolecular energy is determined by the supermolecular approach and the basis set superposition error is corrected by the counterpoise method. Bond functions are found useful and very effective in recovering the dispersion energy, which is traditionally achieved by polarization functions. The calculated binding energy of the water dimer is systematically converged to a value of 4.75 kcal mol⁻ as bond functions are gradually added to nucleus-centered basis sets.     

On the Reliability of the AMBER Force Field and its Empirical Dispersion Contribution for the Description of Noncovalent Complexes

The reliability of the AMBER force field is tested by comparing the total interaction energy and dispersion energy with the reference data obtained at the density functional theory–symmetry‐adapted perturbation treatment (DFT–SAPT)/aug‐cc‐pVDZ level. The comparison is made for 194 different geometries of noncovalent complexes (H‐bonded, stacked, mixed, and dispersion‐bound), at the equilibrium distances as well as at longer distances (up to a relative distance of two). The total interaction energies agree very well with the reference data and only the strength of H‐bonded complexes is slightly underestimated. In the case of dispersion energy, the overall agreement is even better, with the exception of the stacked aromatic systems, where the empirical dispersion energy is overestimated. The use of AMBER interaction energy and AMBER dispersion energy for different types of noncovalent complexes at equilibrium as well as at longer distances is thus justified, except for a few cases, such as the water molecule, where the dispersion energy is highly inaccurate.     

计算液态混合物内能和内压的统计热力学理论

假定二元液态混合物分子间的相互作用势能可以表示成多体相互作用势能的和,分子间的力为短程力,相互作用势能只与分子间的相对距离有关.利用分布函数理论导出了二元液态混合物的过剩内能和内压的公式.二元液态混合物的过剩内能和内压可以表示成体积的幂级数形式,其中的系数可以用多体相互作用势和多体径向分布函数表出.讨论了单元液体的内压和过剩内能的表达式,在两种特殊情形下,过剩内能和内压的表达式分别与Egelstaff的微扰论结果及Frank的实验结果具有相同的形式.讨论了二元混合物内压和内能的两个特例,其一,在特殊情形下,给出了混合液体过剩内能的混合规则的一个证明.其二,给出的二元混合物的过剩内能和内压的表达式与Frank的实验结果具有相同的形式.     

Energy analysis of weak electron-donor-acceptor complexes and water clusters with the perturbation theory based on the locally projected molecular orbitals: charge-transfer and dispersion terms

The third order single excitation perturbation theory corrected with the dispersion energy based on the locally projected molecular orbital was applied to study the weak electron-donor-acceptor (charge-transfer) complexes and the hydrogen bonds in the water clusters. In the weak electron-donor-acceptor complexes, the dispersion energy is larger than the charge-transfer energy in absolute value. The dispersion energy is as large as the charge-transfer energy in the hydrogen bond. The cage form of (H(2)O)(6) is the most stable among eight isomers examined, because the dispersion energy is the largest among them.     

The Influence of the Exchange-Correlation Functional on the Non-Interacting Kinetic Energy and Its Implications for Orbital-Free Density Functional ApproximationsSCI北大核心CSCD

In this work it is shown that the kinetic energy and the exchange-correlation energy are mutual dependent on each other.This aspect is first derived in an orbital-free context.It is shown that the total Fermi potential depends on the density only,the individual parts,the Pauli kinetic energy and the exchange-correlation energy,however,are orbital dependent and as such mutually influence each other.The numerical investigation is performed for the orbital-based non-interacting Kohn-Sham system in order to avoid additional effects due to further approximations of the kinetic energy.The numerical influence of the exchange-correlation functional on the non-interacting kinetic energy is shown to be of the orderof a few Hartrees.For chemical purposes,however,the energetic performance as a function of the nuclear coordinates is much more important than total energies.Therefore,the effect on the bond dissociation curve was studied exemplarily for the carbon monoxide.The data reveals that,the mutual influence between the exchange-correlation functional and the kinetic energy has a significant influence on bond dissociation energies and bond distances.Therefore,the effect of the exchange-correlation treatment must be considered in the design of orbital-free density functional approximations for the kinetic energy.     

导电高聚物聚吡啶的电子能带及其结构研究

聚吡啶(简称PPy)易于进行n-型掺杂并使其电导率大大提高,可用于制作高聚物电池的负极,本文将PPy视为准一维体系,采用EHMO/CO方法计算了新合成的导电高分子材料--聚吡啶4种可能构型的电子能带。     

Nonadditivity of the SCF interaction energy in the (LiH)3 complex

The role of nonadditivity of the interaction energy between three LiH molecules was investigated within the SCF ab initio framework. The nonadditive part of the interaction energy is more important in the case of a cyclic structure than in a linear trimer, and is stabilizing in both cases. The value of the ratio of three-body and two-body terms for different points on the energy hypersurface is discussed.     

Analysis of the chemical bond

The energy expression of the MO-LCAO scheme is corrected approximately for the left-right correlation such that it leads to the correct dissociation limit. Together with the correlation correction a correction is applied to the interference term, whereas the sharing penetration effects are neglected. The derivation of this corrected approximate energy formula is suggested from an analysis of binding in H₂ ⁺ and H₂. The binding energy consists mainly of three contributions: interference, quasiclassical interaction, promotion. Two-electron interference contributions are absorbed into the one-electron terms. The basis dependence of the fragmentation of the binding energy is discussed and an appropriate hybrid basis is constructed. Rotational invariance is found to a high degree of accuracy. In terms of the proposed scheme the binding in several diatomic and polyatomic molecules is analysed. The individual contributions to the binding energy turn out to be physically meaningful.     

A new iterative linear integral isoconversional method for the determination of the activation energy varying with the conversion degree

The conventional linear integral isoconversional methods may lead to important errors in the determination of the activation energy when the significant variation of the activation energy with the conversion degree occurs. Vyazovkin proposed an advanced nonlinear isoconversional method, which allows the activation energy to be accurately determined [Vyazovkin, J Comput Chem 2001, 22, 178]. However, the use of the Vyazovkin method raises the problem of the time‐consuming minimization without derivatives. A new iterative linear integral isoconversional method for the determination of the activation energy as a function of the conversion degree has been proposed, which is capable of providing valid values of the activation energy even if the latter strongly varies with the conversion degree. Also, the new method leads to the correct values of the activation energy in much less time than the Vyazovkin method. The application of the new method is illustrated by processing of theoretically simulated data of a strongly varying activation energy process. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Application of the golden section search algorithm in the nonlinear isoconversional calculations to the determination of the activation energy from nonisothermal kinetic conversion data

In this study, the golden section search algorithm in the nonlinear isoconversional calculations to be used for the determination of the activation energy from nonisothermal kinetic conversion data has been introduced. The technique has been applied to two simulated processes (one corresponds to a constant activation energy process, and the other corresponds to a varying activation energy process) and cellulose pyrolysis. The results have shown that the golden section search algorithm is capable of providing the valid activation energy values.     

On the size dependence of the surface energy of metal nanoclusters

The many-particle tight-binding potential has been employed to calculate the specific surface energy of icosahedral nanoclusters of transition metals. The equimolecular surface has been considered as the dividing surface. The surface energy has been shown to linearly increase with particle size at nanocluster radii smaller than five radii of the first coordination sphere. As the nanocluster radius is further enlarged, the surface energy passes through a maximum and approaches an asymptotic macroscopic value. The coefficients of proportionality between the specific surface energy and nanocluster radius have been found and compared with the data available from the literature.     

On the equivalence between the energy and virial routes to the equation of state of hard-sphere fluids

The energy route to the equation of state of hard-sphere fluids is ill defined since the internal energy is just that of an ideal gas, and thus it is independent of density. It is shown that this ambiguity can be avoided by considering a square-shoulder interaction and taking the limit of vanishing shoulder width. The resulting hard-sphere equation of state coincides exactly with the one obtained through the virial route. Therefore, the energy and virial routes to the equation of state of hard-sphere fluids can be considered as equivalent.     

Might the difference between Schrödinger and Ruedenberg's local contributions to the kinetic energy represent elastic deformations of the electron?

In Schrödinger's equation, the local contribution to the kinetic energy is sometimes negative, but it allows a conservative potential in contrast to an alternative, never negative, energy proposed by Ruedenberg. The total kinetic energy evaluated in certain characteristic volumes, and in all of space, is identical in the two cases. Dirac's suggestion in 1962 of a bubble-surface representing the electron is applied in a far-reaching, but incomplete, attempt to identify external kinetic energy with a first-order relativistic effect and the internal energy constituting the difference between Schrödinger and Ruedenberg's proposals is related to oscillations of the surface.     

Solar Electricity and Solar Fuels: Status and Perspectives in the Context of the Energy Transition

The energy transition from fossil fuels to renewables is already ongoing, but it will be a long and difficult process because the energy system is a gigantic and complex machine. Key renewable energy production data show the remarkable growth of solar electricity technologies and indicate that crystalline silicon photovoltaics (PV) and wind turbines are the workhorses of the first wave of renewable energy deployment on the TW scale around the globe. The other PV alternatives (e.g., copper/indium/gallium/selenide (CIGS) or CdTe), along with other less mature options, are critically analyzed. As far as fuels are concerned, the situation is significantly more complex because making chemicals with sunshine is far more complicated than generating electric current. The prime solar artificial fuel is molecular hydrogen, which is characterized by an excellent combination of chemical and physical properties. The routes to make it from solar energy (photoelectrochemical cells (PEC), dye‐sensitized photoelectrochemical cells (DSPEC), PV electrolyzers) and then synthetic liquid fuels are presented, with discussion on economic aspects. The interconversion between electricity and hydrogen, two energy carriers directly produced by sunlight, will be a key tool to distribute renewable energies with the highest flexibility. The discussion takes into account two concepts that are often overlooked: the energy return on investment (EROI) and the limited availability of natural resources—particularly minerals—which are needed to manufacture energy converters and storage devices on a multi‐TW scale.     

储氢材料的研究进展

日益严峻的能源危机和环境污染,使得发展清洁的可再生能源成为世界各国的重要课题。氢能源以其可再生性和良好的环保效应成为未来最具发展潜力的能源载体,氢能被公认为人类未来的理想能源,而氢的储存是发展氢能技术的难点之一。介绍了各类材料的储氢功能特点和近年来几类主要储氢材料的研究进展,并指出了储氢材料的发展方向。     

The Meaning and Use of the Arrhenius Activation Energy

The nature of the Arrhenius activation energy and frequency factor is reexamined in terms of information now becoming available on the microscopic aspects of collisional reactions. It is pointed out that the activation energy is not generally equal to the threshold for reaction, and its correct conceptual meaning is discussed. The temperature dependence of this quantity and its relation to the threshold energy is developed for a number of representative forms of the energy dependence of the reaction cross-section (excitation function). The uses and limitations of the activation energy as a means of evaluating thresholds, excitation functions, and the presence of tunneling processes are discussed.     

The influence of ion beam sputtering on the composition of the near-surface region of silicon carbide layers

The concentrations and the lattice structure of silicon carbide layers and single crystals are influenced by ion beam sputtering. The influence of ion beam sputtering and primary ion energy on preferential sputtering is investigated by Auger measurements and T-DYN simulations. In dependence on primary ion energy C is enriched. Preferential sputtering increases with decreasing ion energy. Sputtering has a strong influence on the Auger peak shapes of SiC. Except for low ion energy and glancing incidence the peak shapes are independent of the primary ion energy. T-DYN simulations help to explain and understand the near-surface processes during sputtering of SiC. For ion energy dependence of preferential sputtering there is a good agreement of the T-DYN simulation and the Auger measurement. Received: 10 October 1998 / Revised: 26 March 1999 / Accepted: 2 April 1999     

A study of the AMO method as applied to the lithium metal. I. Review,results, and discussion

The total electronic energy per atom in the lithium metal has been calculated for three different Fermi surfaces as a function of the internuclear distance. In each case the optimized AMO energy as well as the total energy corresponding to doubly filled molecular orbitals (MO ) has been calculated. For densities around the equilibrium density the spherical Fermi surface yields the lowest energy whereas a cubic Fermi surface is preferred for low densities. For densities around the equilibrium there is no band splitting: the AMO energy coincides with the MO energy. The computations have been carried out within an LCAO approximation with overlap and multicenter-integrals calculated accurately.