Application of the FAKE molecular-orbital method to diatomic molecules XY (X,Y = H,F, Cl,Br, I)

Theoretical Chemistry Accounts - The FAKE (fast, accurate kinetic energy) method of semiempirical molecular orbital calculation is applied to diatomic molecules XY (X, Y= H, F, Cl, Br, I). The...     

Expansion of atomic orbital products in terms of a complete function set

Summary An alternative method for the evaluation of matrix elements required in an LCAO-SCF calculation is presented. It is based on the use of solutions of the Helmholtz equation within a spherical domain for expanding charge distributions with boundary conditions devised to make the electrostatic-potential integral particularly simple. This method allows the systematic evaluation of bielectronic integrals to be performed for any type of atomic orbitals.Part of a PhD Thesis (J.E.P.) to be presented to the UNRC     

Generalized spherical functions in the theory of many-electron atoms

A new method for finding non-relativistic and relativistic wave-functions of an electron moving in the field of a nuclear charge in the jj coupling scheme is proposed. It is based on the usage of generalized spherical functions. The mathematical apparatus necessary to find the expressions for matrix elements of the non-relativistic and relativistic energy or electron transition operators is developed. The formulas obtained for these matrix elements are more convenient than those usually used in jj coupling scheme; only their radial integrals and some phase multipliers depend on orbital quantum numbers.     

Theoretical investigation of hole mobility in 9,10-diphenylanthracene by density functional calculations

The charge transfer property of the 9,10-diphenylanthracene (DPA) single-crystal system was investigated by density functional calculations. The hole mobility of DPA was predicted according to a hopping mechanism and compared with that of two standard organic single-crystal systems, namely, naphthalene and anthracene. The reorganization energy was calculated by the adiabatic potential energy surface method. The electronic coupling matrix elements were calculated by two methods, namely, the energy splitting in dimer (ESD) method and charge transfer integral (CTI) method. Using the coupling matrix calculated by the CTI method, we predicted a hole mobility of 2.15?cm²/(Vs) for DPA, whereas the CTI method gives the values of 0.35 and 1.39?cm²/(Vs) for naphthalene and anthracene, respectively. It is shown that the electronic coupling calculated by the CTI method gives the qualitatively satisfactory result for the hole mobilities of the three single-crystal systems.     

Feasibility of using beryllium as internal reference to reduce non-spectroscopic carbon species matrix effect in the inductively coupled plasma–mass spectrometry (ICP-MS) determination of boron in biological samples

The mechanism by which carbon matrix species cause non-spectroscopic matrix interference on boron (B) and beryllium (Be) during the determination of B in biological samples is investigated. The study indicates that, unlike other matrix species such as Ca and Na that cause non-spectroscopic matrix interference only through space charge effect, carbon species manifest non-spectroscopic interference by two mechanisms. The minor non-spectroscopic interference of carbon is through space charge effect. However, the major non-spectroscopic effect of carbon is by a charge transfer mechanism from C⁺-species to B and Be atoms in the central channel of the plasma discharge. The large difference in the magnitude of the carbon charge transfer non-spectroscopic matrix interference between Be and B makes Be unsuitable as an internal reference for B in solutions containing more than 1500 μg/ml dissolved organic carbon (DOC). This DOC content is approximately half the DOC usually present in the final sample solution for B determination in biological samples. However, Be still acts as a perfect internal reference to B in solution containing matrix elements that exert their non-spectroscopic interference effect through space charge mechanism (such as Na, K, Ca, etc.).     

An empirical charge transfer potential with correct dissociation limits

The empirical valence bond (EVB) method [J. Chem. Phys. 52, 1262 (1970)] has always embodied charge transfer processes. The mechanism of that behavior is examined here and recast for use as a new empirical potential energy surface for large-scale simulations. A two-state model is explored. The main features of the model are: (1) explicit decomposition of the total system electron density is invoked; (2) the charge is defined through the density decomposition into constituent contributions; (3) the charge transfer behavior is controlled through the resonance energy matrix elements which cannot be ignored; and (4) a reference-state approach, similar in spirit to the EVB method, is used to define the resonance state energy contributions in terms of "knowable" quantities. With equal validity, the new potential energy can be expressed as a nonthermal ensemble average with a nonlinear but analytical charge dependence in the occupation number. Dissociation to neutral species for a gas-phase process is preserved. A variant of constrained search density functional theory is advocated as the preferred way to define an energy for a given charge.     

Theoretical Study on the Charge Transport Properties of Coronene and Its Derivatives

Molecular structures, reorganization energies and charge transport matrix elements of coronene and its fluoro-, hydroxyl- and sulfhydryl-substituted derivatives have been studied at the B3LYP/6-31G＊＊ level. Based on the semi-classical model of electron transfer, charge transport rate constants of the title molecules have been calculated. The results indicate that the coronene molecule is helpful to the transport of negative charge, and the transport rate of positive charge is between those of hexaazatriphenylene and triphenylene.     

Estimates of electronic coupling for excess electron transfer in DNA

Electronic coupling V(da) is one of the key parameters that determine the rate of charge transfer through DNA. While there have been several computational studies of V(da) for hole transfer, estimates of electronic couplings for excess electron transfer (ET) in DNA remain unavailable. In the paper, an efficient strategy is established for calculating the ET matrix elements between base pairs in a pi stack. Two approaches are considered. First, we employ the diabatic-state (DS) method in which donor and acceptor are represented with radical anions of the canonical base pairs adenine-thymine (AT) and guanine-cytosine (GC). In this approach, similar values of V(da) are obtained with the standard 6-31G(*) and extended 6-31+ +G(**) basis sets. Second, the electronic couplings are derived from lowest unoccupied molecular orbitals (LUMOs) of neutral systems by using the generalized Mulliken-Hush or fragment charge methods. Because the radical-anion states of AT and GC are well reproduced by LUMOs of the neutral base pairs calculated without diffuse functions, the estimated values of V(da) are in good agreement with the couplings obtained for radical-anion states using the DS method. However, when the calculation of a neutral stack is carried out with diffuse functions, LUMOs of the system exhibit the dipole-bound character and cannot be used for estimating electronic couplings. Our calculations suggest that the ET matrix elements V(da) for models containing intrastrand thymine and cytosine bases are essentially larger than the couplings in complexes with interstrand pyrimidine bases. The matrix elements for excess electron transfer are found to be considerably smaller than the corresponding values for hole transfer and to be very responsive to structural changes in a DNA stack.     

Quantum chemical study on excited states and charge transfer of oxazolo[4,5-b]-pyridine derivatives

The excitedstate intramolecular charge transfer of four oxazolo[4,5-b]pyridine derivatives with different electron donating and electron withdrawing groups was investigated using the time-dependent density functional theory. The vertical excitation energies and the electronic structures were explored. Their distinct properties of absorption and fluorescence spectra in solvent phase were explained according to the electronic coupling matrix elements calculated by the Mulliken-Hush theory. The sub-stituent on the oxazolo[4,5-b]pyridines will remarkably change their spectra properties and increase the first excited-state dipole moments. The effect of protonation on the absorption and fluorescence spectra was also investigated systematically. Our study suggests that the present method is feasible to explain charge transfer excitation and predict the properties of absorption and emission spectra in the studied systems.     

Theoretical study of substituent effect on the charge mobility of 2,5-bis(trialkylsilylethynyl)-1,1,3,4-tetraphenylsiloles

The theoretical calculation of the charge mobility of 2,5-bis(trialkylsilylethynyl)-1,1,3,4-tetraphenylsiloles is presented. B3LYP/6-31* calculations demonstrated that these silole molecules possessed large coupling matrix elements and reorganization energies for electron and hole transfers and high electron mobilities. The bulkiness of the trialkyl substituents influenced the charge mobility of the silole molecules, with the smaller trimethyl group imparting higher charge mobility than triethyl and triisopropyl substituents.     

A fast and Space-efficient boundary element method for computing electrostatic and hydration effects in large molecules

At present, there are two widely used approaches for computing molecular hydration and electrostatic effects within the continuum approximation: the finite difference method, in which the electric potential is directly computed on a cubic grid, and the induced polarization charge or boundary element method, in which an induced charge distribution is first computed on the molecular surface and in which solvation effects are then calculated by reference to the reaction field arising from this induced surface charge. While the induced surface charge approach has a number of advantages over finite differences, especially in the computation of hydration forces and solvent stabilization, the applications of this technique have been largely restricted to small molecules. This is primarily due to the very large system of equations that results when the surface of a macromolecule is discretized into elements small enough to ensure an acceptable level of numerical accuracy within the continuum model. This article describes a new algorithm for implementing boundary element calculations within the continuum model. The essence of our approach is only to compute explicitly those interactions between surface elements that are relatively close together and to approximate long-range interactions by grid-based multipole expansion. The resulting system of equations has a relatively sparse coefficient matrix and requires disk storage that increases linearly with molecular surface area. The technique has numerous applications in the analysis of solvation effects in large molecules, especially in the area of conformational analysis, where it is critical to accurately estimate the global hydration energy for the entire structure. © 1996 by John Wiley & Sons, Inc.     

9,10-二氰基蒽和杜烯间光诱导电子转移的电荷分离态和电子耦合

采用从头算方法,讨论了9,10-二氰基蒽(DCA)和杜烯(DUR)间光诱导电子转移反应的态-态跃迁.考虑基组重叠误差(BSSE)对相互作用能的校正,用MP₂方法优化得到重叠式[DCA…DUR]配合物的稳定构型.用单激发组态相互作用(CIS)方法讨论了[DCA…DUR]配合物的光诱导电荷分离和电荷复合过程.根据广义Mulliken-Hush(GMH)模型,计算了电荷复合过程的电子耦合矩阵元.结果表明,[DCA…DUR]配合物的S₀→S₁和S₀→S₂跃迁产生了两个强的局域激发态,S₀→S₃跃迁直接导致电荷分离态,小的振子强度预测该电荷转移(CT)跃迁是一弱跃迁,电荷分离态S₃衰变到低局域激发态或基态的电荷复合是可能的.     

Some theoretical remarks about semiempirical calculation of quadrupolar moments

The theory of quadrupolar moments evaluation at a Semiempirical level is examined in great detail. Special attention is devoted to the way proposed for the estimation of the sigma contribution using the point charge approximation, and to the neglect of nearest-neighbour matrix elements in the evaluation of the property when wave functions obtained using the ZDO approximation are used. There are objections to both procedures. In the last case a study of a method to evaluate these contributions, based on a reinterpretation of the ZDO approximation in terms of a symmetric orthogonalized basis set, is carried out.     

Theoretical investigation of charge transfer excitation and charge recombination in acenaphthylene–tetracyanoethylene complex

Ab initio calculations were performed to investigate the charge separation and charge recombination processes in the photoinduced electron transfer reaction between tetracyanoethylene and acenaphthylene. The excited states of the charge‐balanced electron donor–acceptor complex and the singlet state of ion pair complex were studied by employing configuration interaction singles method. The equilibrium geometry of electron donor–acceptor complex was obtained by the second‐order Møller–Plesset method, with the interaction energy corrected by the counterpoise method. The theoretical study of ground state and excited states of electron donor–acceptor complex in this work reveals that the S₁ and S₂ states of the electron donor–acceptor complexes are excited charge transfer states, and charge transfer absorptions that corresponds to the S₀ → S₁ and S₀ → S₂ transitions arise from π–π* excitations. The charge recombination in the ion pair complex will produce the charge‐balanced ground state or excited triplet state. According to the generalized Mulliken–Hush model, the electron coupling matrix elements of the charge separation process and the charge recombination process were obtained. Based on the continuum model, charge transfer absorption and charge transfer emission in the polar solvent of 1,2‐dichloroethane were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 23–35, 2003     

氟化电热蒸发／电感耦合等离子体原子发射光谱中的基体效应研究

本文系统研究了氟化电热蒸发／电感耦合等离子体原子发射光谱（ＥＴＶ－ＩＣＰ－ＡＥＳ）测定难熔元素的基体效应。与常规气动雾化（ＰＮ）－ＩＣＰ－ＡＥＳ中的基体效应比较，氟化ＥＴＶ－ＩＣＰ－ＡＥＳ中的基体效应更小。对难熔基体元素，由于基体和待测元素与氟化剂之间的竞争反应，随着基体浓度的增加，待测元素谱线强度降低；对常见基体元素，由于热循环中基体与待测元素之间的选择挥发，对待测元素的蒸发和传输过程无明显影响     

Glow discharge excitation and matrix effects in the Zn–Al–Cu system in argon and neon

Matrix effects and other deviations from the standard model of glow discharge optical emission spectroscopy (GD-OES) have been investigated in the Zn–Al–Cu system in a Grimm-type discharge in argon and neon. In ionic spectra of the elements that can be ionized by asymmetric charge transfer with ions of the discharge gas, most observed deviations from the standard model can be explained by variations of the number density of ions of the discharge gas, caused by asymmetric charge transfer reactions with the matrix element. Similar mechanism, but involving metastables of the discharge gas, was observed for the Cu II spectrum in neon. Some matrix effects in atomic spectra of aluminium and possibly also copper suggest that three-body recombination of ions of the discharge gas, assisted by an analyte atom, is responsible for excitation of certain atomic levels of the analyzed elements. Excited atomic states of the analyzed elements have higher fractional populations in neon than argon, by factors that are similar for all three elements and the median of which is slightly less than 3. It is shown which lines are free of matrix effects and suitable for highly accurate analysis of Zn–Al–Cu alloys by GD-OES and how to optimize the calibration model. Neon can be a reasonable alternative to argon as the discharge gas for some applications.     

Generalized Mulliken-Hush analysis of electronic coupling interactions in compressed pi-stacked porphyrin-bridge-quinone systems

Donor-acceptor interactions were investigated in a series of unusually rigid, cofacially compressed pi-stacked porphyrin-bridge-quinone systems. The two-state generalized Mulliken-Hush (GMH) approach was used to compute the coupling matrix elements. The theoretical coupling values evaluated with the GMH method were obtained from configuration interaction calculations using the INDO/S method. The results of this analysis are consistent with the comparatively soft distance dependences observed for both the charge separation and charge recombination reactions. Theoretical studies of model structures indicate that the phenyl units dominate the mediation of the donor-acceptor coupling and that the relatively weak exponential decay of rate with distance arises from the compression of this pi-electron stack.     

Solution of periodic Poisson's equation and the Hartree–Fock approach for solids with extended electron states: Application to linear augmented plane wave method

We formulate a Hartree–Fock‐LAPW method for electronic band structure calculations. The method is based on the Hartree–Fock–Roothaan approach for solids with extended electron states and closed core shells where the basis functions of itinerant electrons are linear augmented plane waves. All interactions within the restricted Hartree–Fock approach are analyzed and in principle can be taken into account. In particular, we obtained the matrix elements for the exchange interactions of extended states and the crystal electric field effects. To calculate the matrix elements of exchange for extended states, we first introduce an auxiliary potential and then integrate it with an effective charge density corresponding to the electron exchange transition under consideration. The problem of finding the auxiliary potential is solved by using the strategy of the full potential LAPW approach, which is based on the general solution of periodic Poisson's equation. Here, we use an original technique for the general solution of periodic Poisson's equation and multipole expansions of electron densities. We apply the technique to obtain periodic potentials of the face‐centered cubic lattice and discuss its accuracy and convergence in comparison with other methods. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Quantum-Chemical Calculation of Matrix Elements in a Basis of Functions with Polynomial Tails

A numerical integration method is suggested for calculating Hamiltonian matrix elements in a basis of functions with polynomial tails with allowance for discontinuities of higher-order derivatives of the basis function within the domain of integration. The method is tested by calculating matrix elements for a copper crystal. The results for the overlap matrix elements are presented demonstrating efficiency of the method.