Self-consistent fluid variational theory for the dissociation of dense nitrogen

The self-consistent fluid variational theory is used to calculate the pressure dissociation of dense nitrogen at high temperatures. The accurate high-pressure and high-temperature effective pair potentials are adopted to describe the intermolecular interactions, which are made to consider molecular dissociation. This paper focuses on a mixture of nitrogen atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperature. The equation of state and dissociation degree are calculated from the free-energy functions in the range of temperature of 2000-15 000 K and density of 0.2-3.0 gcm(3), which can be compared with other approaches and experiments.     

Probing the mechanism of hypoxia selectivity of copper bis(thiosemicarbazonato) complexes: DFT calculation of redox potentials and absolute acidities in solution

Density functional theory (DFT) calculations have been performed using the uB3LYP/6-31++G(d,p) model to calculate the solution phase one-electron reduction potentials (E(calc)) and absolute pKa values of a series of copper bis(thiosemicarbazonato) complexes. The effects of solvation in water and dimethylsulfoxide (DMSO) are incorporated as a self-consistent reaction field (SCRF) using the integral equation formalism polarisable continuum model (IEFPCM) and are found to be essential for quantitative agreement with an average error in E(calc) of -0.02 V compared to experiment. The bonding and spin densities are examined through the use of Natural Bond Order analysis and the results used to rationalise the calculated and observed reduction potentials. Calculated estimates of pKa values of several copper(II) species are presented and their implications for the mechanisms of transport and trapping within hypoxic cells are considered. Reduction is found to be a prerequisite for protonation of the complexes which suggests their transport in the blood stream as neutral species, and the mechanistic sequence is identified as a sequential electrochemical-chemical (EC) process. The complex equilibria of protonation, reoxidation and dissociation are discussed and the copper(I) diprotonated, cationic complex of diacetyl bis(4-methyl-3-thiosemicarbazonato)copper(II), Cu(I)ATSMH2(+), is identified as a possible candidate for the initial species trapped in hypoxic cells.     

Excitation energy transfer (EET) between molecules in condensed matter: a novel application of the polarizable continuum model (PCM)

We present a quantum-mechanical theory to study excitation energy transfers between molecular systems in solution. The model is developed within the time-dependent (TD) density-functional theory and the solvent effects are introduced in terms of the polarizable continuum model (PCM). Unique characteristic of this model is that both "reaction field" and screening effects are included in a coherent and self-consistent way. This is obtained by introducing proper solvent-specific operators in the Kohn-Sham equations and in the corresponding TD scheme. The solvation model exploits the integral equation formalism (IEF) version of PCM and it defines the solvent operators on a molecular cavity modeled on the real three-dimensional (3D) structure of the solute systems. Applications to EET in dimers of ethylene and naphtalene are presented and discussed.     

Towards a quantum-chemical representation of enzyme activity. A scrf pce cndo/2 study of the ladh proton relay system

The proton translocation process via the proton relay system of LADH has been studied within the self-consistent reaction field protein core effect (SCRF PCE) theory. The inhomogeneous electric field of the protein atoms, other than those belonging to the cage system, the Zn atom and the NAD⁺ coenzyme, have been let in step by step; the polarization reaction field is being allowed for at the last stage. The spatial charge-separation process appearing in the LADH action mechanism is substantiated by the present calculations. These results strongly suggest that the proposed scheme would be a faithful representation of some of the enzyme activity factors.     

Double proton transfer behavior and one-electron oxidation effect in double H-bonded glycinamide-formic acid complex

The behavior of double proton transfer occurring in a representative glycinamide-formic acid complex has been investigated at the B3LYP/6-311 + + G( * *) level of theory. Thermodynamic and, especially, kinetic parameters, such as tautomeric energy, equilibrium constant, and barrier heights have been discussed, respectively. The relevant quantities involved in the double proton transfer process, such as geometrical changes, interaction energies, and intrinsic reaction coordinate calculations have also been studied. Computational results show that the participation of a formic acid molecule favors the proceeding of the proton transfer for glycinamide compared with that without mediate-assisted case. The double proton transfer process proceeds with a concerted mechanism rather than a stepwise one since no ion-pair complexes have been located during the proton transfer process. The calculated barrier heights are 11.48 and 0.85 kcal/mol for the forward and reverse directions, respectively. However, both of them have been reduced by 2.95 and 2.61 kcal/mol to 8.53 and -1.76 kcal/mol if further inclusion of zero-point vibrational energy corrections, where the negative barrier height implies that the reverse reaction should proceed with barrierless spontaneously, analogous to that occurring between glycinamide and formamide. Furthermore, solvent effects on the thermodynamic and kinetic processes have also been predicted qualitatively employing the isodensity surface polarized continuum model within the framework of the self-consistent reaction field theory. Additionally, the oxidation process for the double H-bonded glycinamide-formic acid complex has also been investigated. Contrary to that neutral form possessing a pair of two parallel intermolecular H bonds, only a single H bond with a comparable strength has been found in its ionized form. The vertical and adiabatic ionization potentials for the neutral complex have been determined to be about 9.40 and 8.69 eV, respectively, where ionization is mainly localized on the glycinamide fragment. Like that ionized glycinamide-formamide complex, the proton transfer in the ionized complex is characterized by a single-well potential, implying that the proton initially attached to amide N4 in the glycinamide fragment cannot be transferred to carbonyl O13 in the formic acid fragment at the geometry of the optimized complex.     

Multiconfiguration self-consistent field,theory of localized orbitals: Choice of localization potential

We investigate the properties of two different choices for localization potentials for the direct construction of localized fixed orbitals by multiconfiguration self-consistent field theory. The first potential yields maximally screened orbitals by solution of a complicated orbital equation which depends explicitly on the complete set of orbitals for the system, and contains both one-and two-center matrix elements. The second localization potential yields somewhat less well screened orbitals by solution of a considerably simpler orbital equation which only contains simple one-center matrix elements.     

Interaction between charge-regulated surfaces in the presence of polyelectrolytes

This work gives a brief overview of the backgrounds of the self-consistent mean-field theory as applied to the problem of interaction between charge-regulated surfaces in the presence of polyelectrolytes. A general algorithm for obtaining a self-consistent solution is described, and the asymptotic properties of the solution at close separations are analyzed. Known limitations of the self-consistent field approximation are discussed, highlighting the role of local effects and system equilibration.

     

Computational study of the ion-molecule reactions involving fluxional cations: CH4+ + H2--> CH5+ + H and isotope effect

Potential energy surfaces for the reactions of CH4+ with H2, HD, and D2 have been calculated using high-level ab initio methods, including coupled cluster theory, complete active space self-consistent field, and multireference configuration interaction. The energies are extrapolated to the complete basis set limit using the basis sets aug-cc-pVXZ (X = D, T, Q, 5, 6). The CH4+ + H2 reaction produces CH5+ and H exclusively. Three types of reaction mechanisms have been found, namely, complex-forming abstraction, scrambling, and S(N)2 displacement. The abstraction occurs via a very minor barrier and it is dominant. The other two mechanisms are negligible because of the significant barriers involved. Quantum phase space theory and variational transition state theory are used to calculate the rate coefficients as a function of temperatures in the range of 5-1000 K. The theoretical rate coefficients are compared with the available experimental data and the discrepancy is discussed. The significance of isotope effect, tunneling effect, and nuclear spin effect is investigated. The title reaction is predicted to be slightly exothermic with DeltaHr = -12.7 +/- 5.2 kJ/mol at 0 K.     

Uniqueness of the iterative solution of the optimized effective potential equation

The optimized effective potential (OEP) equation can be used in a numerically efficient self-consistent form to solve for the density functional exchange and correlation potentials, as shown in a recent paper of Kummel and Perdew [Phys. Rev. Lett. 90, 43004 (2003)]. The uniqueness of an iterative solution of the OEP equation has not yet been adequately addressed. In this paper, it is shown that no nonconstant multiplicative potentials that can contaminate an iterative solution of the OEP equation exist and, hence, that formally the exact exchange-correlation potential determined form of the OEP equation is unique to within a constant.     

Ionization potentials,electron affinities,electronegativities, and hardnesses of fractional charged atoms from the density-functional theory

The electron-correlation and self-interaction corrected generalized exchange local-spin-density functional theory with the Gopinathan, Whitehead, and Bogdanovic Fermi-hole parameters has been employed to give self-consistent field calculations for the quark atoms, the first- and second-order positive ions, and the first- and second-order negative ions of the quark atoms with fractional nuclear charges $ Z = N \pm \frac{1}{3} $ and $ Z = N \pm \frac{2}{3} $. A special technique to obtain the converged second-order negative ions is discussed. The first and second ionization potentials and electron affinities are calculated by the differences of the total energies between the ionized and nonionized systems and compared with the empirical inter-extrapolation results. The agreement between the present calculations and the inter-extrapolated results is excellent for the ionization potentials and reasonably good for the electron affinities of the quark atoms. Finally, the calculated ionization potentials and electron affinities are used in obtaining the electronegativities and hardnesses for these quark atoms.     

柔性高分子/小分子液晶混合物的自洽场理论

发展了柔性高分子/小分子液晶混合物连续自洽场理论，将小分子液晶模型化 为取向与位置无关的单体分子，小分子液晶间存在各向异性的Maier-Saupe相互作 用，该理论可还原成高分子和各向同性小分子组成的Flory-Huggins溶液理论和纯 液晶的Maier-Squpe液晶理论，通过数值解自洽场方程组，还将理论用于研究柔性 高分子/小分子液晶混合物相分离开界面性质，得到的结果与用Helfand格子界面理 论和MOnte Carlo模拟的结果一致。     

Relativistic all-electron configuration interaction calculations on the gold atom

We present the results of relativistic and non-relativistic self-consistent field and configuration interaction calculations for the gold atom, using the spin-free no-pair Hamiltonian in a basis set expansion. A new basis set for the gold atom is discussed and its results in relativistic and non-relativistic self-consistent field calculations are compared to those of numerical Dirac-Hartree-Focic and Hartree-Fock calculations, respectively. Excitation energies, electron affinities and ionization potentials were calculated using a multi-reference configuration interaction technique and are in reasonable agreement with experiment in the relativistic case.     

Theoretical study on the properties of linear and cyclic amides in gas phase and water solution

The structural and energetic properties of a group of selected amides, of well-known importance for the design of efficient clathrate inhibitors, are calculated with Hartree-Fock and density functional theory, B3LYP, theoretical levels, and a 6-311++g** basis set in the gas phase and a water solution. The conformational behavior of the molecules is studied through the scanning of the torsional potential energy surfaces and by the analysis of the differences in the energetic and structural properties between the isomers. The properties of the amides in water solution are determined within a self-consistent reaction field approach with a polarizable continuum model that allows the calculation of the different contributions to the free energy of solvation. The calculated barriers to rotation are in good agreement with the available experimental data and the comparison of the gas and water results shows the strong effect of the solute polarization. The properties of different amide-water complexes are calculated and compared with available experimental information.     

Variational calculation of vibrational linear and nonlinear optical properties

A variational approach for reliably calculating vibrational linear and nonlinear optical properties of molecules with large electrical and/or mechanical anharmonicity is introduced. This approach utilizes a self-consistent solution of the vibrational Schrodinger equation for the complete field-dependent potential-energy surface and, then, adds higher-level vibrational correlation corrections as desired. An initial application is made to static properties for three molecules of widely varying anharmonicity using the lowest-level vibrational correlation treatment (i.e., vibrational M?ller-Plesset perturbation theory). Our results indicate when the conventional Bishop-Kirtman perturbation method can be expected to break down and when high-level vibrational correlation methods are likely to be required. Future improvements and extensions are discussed.     

Equation of state for expanded fluid mercury: variational theory with many-body interaction

A variational associating fluid theory is proposed to describe equations of state for expanded fluid mercury. The theory is based on the soft-sphere variational theory, incorporating an ab initio diatomic potential and an attractive many-body potential; the latter is evaluated with quantum chemical methods and expressed as a function of the local atomic coordination number and the nearest-neighbor distance. The resultant equation of state can reproduce the observed gas-liquid coexistence curve with good accuracy, without introducing phenomenological effective pair potentials. Various thermodynamic quantities such as pressure, isocloric thermal pressure coefficient, adiabatic sound velocity, and specific heat are calculated over a wide density-temperature range and compared with available experimental data.     

Accurate calculation of core-electron binding energies: multireference perturbation treatment

Multireference perturbation theory (MRPT) with multiconfigurational self-consistent field (MCSCF) reference functions is applied to the calculations of core-electron binding energies (CEBEs) of atoms and molecules. Orbital relaxations in a core-ionized state and electron correlation are both taken into account in a conventional MCSCF-MRPT procedure. In the MCSCF calculation, the target core ionized state is directly optimized as an excited state and this treatment can completely prevent a variational collapse. Multireference Moller-Plesset perturbation theory and multiconfigurational self-consistent field reference quasidegenerated perturbation theory were used to treat electron correlation. The present method quite accurately reproduced the 1s CEBEs of CH4, NH3, H2O, and FH; the average deviation from the experimental data is 0.11 eV using Ahlrichs' VTZ basis set. The C 1s and O 1s CEBEs of formic acid and acetic acid were calculated and the results are consistent with the bonding characters of the atoms in these molecules. The present procedure can also be applied to CEBEs of higher angular momentum orbitals by including spin-orbit coupling. The calculated CEBEs of Ar 2p, HCl 2p, Kr 3d, and HBr 3d are in reasonable agreement with the available experimental values. In the calculation of the 3d CEBEs, a relativistic correction significantly improves the agreements. The effect of polarization functions is also discussed.     

Effective intramolecular interactions in weakly charged polyelectrolytes: Relation to structural behavior of solution

A self-consistent integral equation theory in the form of a hybrid Monte Carlo/PRISM computation scheme was used to study a polyelectrolyte solution. The static conformational and structural properties of polyions of different rigidities in a good solvent were studied with explicit allowance for counterions over a wide concentration range. An analysis of the calculated effective potentials and correlation functions confirms the presence of effective attraction between units of the charged polymer in semidilute and concentrated solutions; this attraction leads to the collapse of polyions under certain conditions. It was shown that the cause of effective attraction is the dipole-dipole interaction of ion pairs. For the region of polyelectrolyte transition from the semidilute to the concentrated state of solution, the results qualitatively agree with experimental data and theoretical predictions. Visualized images of conformations in the test range of parameters are given.     

Theoretical study on electronic and spin structures of [Fe2S2](2+,+) cluster: reference interaction site model self-consistent field (RISM-SCF) and multireference second-order Møller-Plesset perturbation theory (MRMP) approach

Electronic structures of [Fe(2)S(2)(SCH(3))(4)](2-,3-) in DMSO solution are calculated using reference interaction site model complete active space self-consistent field (RISM-CASSCF)/multireference second-order M?ller-Plesset perturbation theory (MRMP) method. For the reduced state, we obtain both the low-spin Fe(3+)Fe(2+) localized and high-spin Fe(2.5+)Fe(2.5+) delocalized forms, which are very close in energy. The spin interaction constants obtained from the energies of states with various spin multiplicities are in good agreement with the available experimental estimates both for the oxidized and for the reduced states. The dynamic electron correlation effect is found to be important in estimating the spin interaction between the Fe ions. The redox potentials are calculated to be 2.87 and 2.78 eV for the localized and delocalized reduced states, respectively, which are close to the experimental values. We devise a simple model for calculating the free energy curves of the reduction process based on the RISM-SCF theory. The activation barrier height is calculated to be 7.4 kcal/mol at the equilibrium geometry of oxidized state, indicating that the reduction reaction will occur efficiently in DMSO solvent. The effect of solvent fluctuation on the free energy profiles is discussed on the basis of the present calculations.     

A self-consistent field procedure for stationary states using an algebraic approach and the maximum entropy formalism

A stationary state of maximal entropy is derived as a solution of a variational procedure. Generators of a continuous group are used as the constraints. The self-consistent hamiltonian is linear in these generators so that the solution of the self-consistency problem is replaced by a solution of an algebraic equation. The familiar Hartree-Fock procedure is a special case.     

Self-consistent, constrained linear-combination-of-atomic-potentials approach to quantum mechanics

Variational fitting gives a stationary linear-combination of atomic potentials (LCAP) approximation to the Kohn-Sham (KS) potential, V. That potential is central to density-functional theory because it generates all orbitals, occupied as well as virtual. Perturbation theory links two self-consistent field (SCF) calculations that differ by the perturbation. Using the same variational LCAP methods and basis sets in the two SCF calculations gives precise KS potentials for each order. Variational V perturbation theory, developed herein through second order, gives stationary potentials at each order and stationary even-order perturbed energies that precisely link the two SCF calculations. Iterative methods are unnecessary because the dimension of the matrix that must be inverted is the KS basis size, not the number of occupied times virtual orbitals of coupled-perturbed methods. With variational perturbation theory, the precision of derivatives and the fidelity of the LCAP KS potential are not related. Finite differences of SCF calculations allow the precision of analytic derivatives from double-precision code to be verified to roughly seven significant digits. For a simple functional, the fourth derivatives of the energy and the first and second derivative of the KS potentials with respect to orbital occupation are computed for a standard set of molecules and basis sets, with and without constraints on the fit to the KS potential. There is no significant difference between the constrained and unconstrained calculations.