Piet Th. van Duijnen

University of Groningen | RUG · Theoretical Chemistry Group

Trends in bond angle are identified in a systematic study of more than a thousand symmetric A2B triatomic molecules. We show that, in series where atoms A and B are each varied within a group, the following trends hold: 1) the A-B-A bond angle decreases for more polarisable central atoms B, and 2) the A-B-A angle increases for more polarisable oute...

The paper reports the results of a theoretical study of the conformational behavior and basicity of biogenic amine agmatine. The complexes modelling of agmatine – protein interaction are also under scrutiny of our investigation using the Becke3LYP and B97D levels of the density functional theory. The relative stabilities (Gibbs energies) of individ...

The thermal metal-insulator phase transition in the π-stacked (EDO-TTF)2PF6 charge transfer salt is of the Peierls type. It is related to geometrical reorganisations and charge ordering phenomena. We report that dimerising displacements are involved in the mechanism of this transition. By using periodic quantum chemical calculations, we find a doub...

The insulating and conducting phases of (EDO-TTF)2PF6 were studied by all electron, periodic Hartree-Fock and hybrid density functional calculations. Electronic properties, such as the electronic band structure, the density of states and the Fermi surface are discussed in relation to the metal-insulator transition in this material. The nature of co...

In this paper we present a theoretical study of the nature of the ground state of the (EDO-TTF)2PF6 charge transfer salt by using ab initio quantum chemical theory for clusters in vacuum, for embedded clusters and for the periodic system. Exemplary for other organic charge transfer systems, we show that by using a relatively low level of theory it...

The polarizability of fullerenes may be used in the design of nanostructures with specific properties and behaviour. Recent studies have been reported on the exaltation of polarizability, for which costly quantum-mechanical studies were needed. Here we report the results of Thole's polarizability model that correctly predicts the exaltation effect...

Screened Coulomb interaction in dielectrics is often used as an argument for a lower exciton binding energy and easier exciton dissociation in a high dielectric material. In this paper, we show that at length scales of excitons (10-20 angstrom), the screened Coulomb law is invalid and a microscopic (quantum chemical) description is necessary to des...

Density functional theory methods with the B3LYP functional have been used to study the acidity of carboxyl, O-sulfo and N-sulfo groups in six basic monomeric structural units of heparin (1-OMe deltaUA-2S, 1-OMe GlcN-S6S, 1,4-DiOMe GlcA, 1,4-DiOMe GlcN-S3S6S, 1,4-DiOMe IdoA-2S, and 1,4-DiOMe GlcN-S6S). The predicted gas-phase acidity of the acidic...

The effects of complexation by Li+, Na+, K+, Mg2+, and Ca2+ counterions and water on the molecular structure of the Fondaparinux pentameter (D–E–F–G–H) and its dimer units (D–E, E–F, F–G and G–H) are studied using Becke 3LYP hybrid density functional theory and molecular modeling. The ionic charge state, the number of metal ion adducts and the coun...

Our work reports in detail the results of systematic large-scale theoretical investigations of the complexes modeling heparin–protein interaction (CH3OSO3−Arg+, CH3NHSO3−Arg+, CH3CO2−Arg+, CH3OSO3−Lys+, CH3NHSO3−Lys+, CH3CO2−Lys+, CH3OPO3H2−Arg+, CH3OPO3H2−Lys+, CH3O(CH3)PO2−Arg+, CH3O(CH3)PO2−Lys+, 1,4-DiOMeIdoA2SNa−Arg+, 1,4-DiOMeIdoA2SNa−Lys+) u...

Our work reports in detail the results of systematic large-scale theoretical investigations of the complexes modeling heparin – protein interaction (CH3OSO3- ···Arg+, CH3NHSO3- ···Arg+, CH3CO2- ···Arg+, CH3OSO3- ···Lys+, CH3NHSO3-···Lys+, CH3CO2-···Lys+, CH3OPO3H2-···Arg+, CH3OPO3H2-···Lys+, CH3O(CH3)PO2- ···Arg+, CH3O(CH3)PO2- ···Lys+, 1,4-DiOMeId...

The geometry of ethylenedioxy-tetrathiafulvalene, EDO-TTF, plays an important role in the metal-insulator transition in the charge transfer salt (EDO-TTF)(2)PF(6). The planar and off-planar geometrical conformations of the EDO-TTF molecules are explained using an extended Debye polarizability model for the bond angle. The geometrical structure of E...

One-electron oxidation of the non-alternant polycyclic aromatic hydrocarbon pleiadiene and related cyclohepta[c,d]pyrene and cyclohepta[c,d]fluoranthene in THF produces corresponding radical cations detectable in the temperature range of 293–263K only on the subsecond time scale of cyclic voltammetry. Although the EPR-active red-coloured pleiadiene...

This study reports in detail the results of sys-tematic large-scale theoretical investigations of the acidic dimeric structural units (D–E, E–F, F–G, and G–H) and pentamer D–E–F–G–H (fondaparinux) of the glycosami-noglycan heparin, and their anionic forms. The geometries and energies of these oligomers have been computed using HF/6–31G(d), Becke3LY...

We present here the discrete reaction field (DRF) approach, which is an accurate and efficient model for studying solvent effects on spectra, chemical reactions, solute properties, etc. The DRF approach uses a polarizable force field, which is (apart from the short-range repulsion) based entirely on second-order perturbation theory, and therefore e...

We performed ab initio quantum chemical calculations for the geometrical and electronic structure of the EDO-TTF (ethylenedioxy-tetrathiafulvalene) molecule using HF, CASSCF and DFT methods. We compare these in vacuo results with the properties of the (EDO-TTF)2PF6 crystal at near room temperature. We demonstrate that, by bending and charging the m...

We report the calculated visible spectrum of [FeIII(PyPepS)2]- in aqueous solution. From all-classical molecular dynamics simulations on the solute and 200 water molecules with a polarizable force field, 25 solute/solvent configurations were chosen at random from a 50 ps production run and subjected the systems to calculations using time-dependent...

DFT was used to investigate molecular structure and metal affinity of the systems CH3CO2M (1), CH3–O–SO3M (2), CH3–NH–SO3M (3), (CH3–O–PO3M)_ (4), CH3–O–PO3M2 (5), CH3–O–(CH3)PO2M (6), and 1,4-DiOMe IdoA-2SM2 (7; 2So conformation) (M = Li+ and Na+), respectively. Interaction enthalpies, entropies and Gibbs energies of the metal-coordinated systems...

Preliminary molecular dynamics simulations of the nematic phase of 4-n-pentyl-4'-cyanobiphenyl are described. The simulations include all molecular degrees of freedom. The influence of the molecular dipole moment is investigated by comparing simulations with and without a charge distribution on the molecules. Inclusion of the charge distribution is...

A molecular model for electronic polarization of water is defined, consisting of interacting point dipole polarizabilities in an electric field generated by atomic point charges, which represent the gasphase dipole moment of water molecules. The induced dipole equations are solved self consistently. The model has been implemented in a Monte Carlo h...

In this chapter we review the discrete solvent reaction field (DRF) model as implemented in time-dependent density functional theory (TD-DFT). The DRF model is a polarizable quantum mechanics/molecular mechanics (QM/MM) model for calculating molecular response properties of molecules in the condensed phase. Using this model effective microscopic pr...

In this work we present calculated absorption and emission spectra in acetonitrile (MeCN) solution of N-acetyl-1-aminopyrene (PAAc, a spectroscopic model compound) and N-(1-pyrenyl)-1-methyluracil-5-carboxamide (PAU(Me), a computational model for 5-(N-carboxyl-1-aminopyrenyl)-2'-deoxyuridine (PAdU)). The computational method used--the discrete reac...

In this work we have investigated the first hyperpolarizability of pNA in 1,4-dioxane solution using a quantum mechanics/molecular mechanics (QM/MM) model. The particular model adopted is the recently developed discrete solvent reaction field (DRF) model. The DRF model is a polarizable QM/MM model in which the QM part is treated using time-dependen...

In this paper the role of the solvent in the formation of the charge-separated excited state of 9,9'-bianthryl (BA) is examined by means of mixed molecular mechanical/quantum mechanical (QM/MM) calculations. It is shown that in weakly polar solvents a relaxed excited state is formed with an interunit angle that is significantly smaller than 90 degr...

We have calculated the frequency-dependent refractive index and the third-order nonlinear susceptibility for C60 in the condensed phase, which is related to third-harmonic generation (THG) and degenerate four-wave mixing (DFWM) experiments. This was done using the recently developed discrete solvent reaction field (DRF) model, which combines a time...

A polarizable quantum mechanics and molecular mechanics model has been extended to account for the difference between the macroscopic electric field and the actual electric field felt by the solute molecule. This enables the calculation of effective microscopic properties which can be related to macroscopic susceptibilities directly comparable with...

Recently we presented an extension of the direct reaction field (DRF) method, in which a quantum system and a set of point charges and interacting polarizabilities are embedded in a continuum that is characterized by a dielectric constant ϵ and a finite ionic strength. The reaction field of the continuum is found by solving the (linearized) Poisson...

This paper describes a quantum chemical study of the electronic structure of thienylene vinylene oligomers ranging in size from two thienylene rings (2TV) to 12TV. The geometries of the TV oligomers in the ground state, the lowest triplet state, and the singly and doubly oxidized states were optimized using density functional theory calculations. T...

Some properties of -helices of polyclycine and polyalanine, up to the decapeptide, were investigated by ab initio molecular-orbital calculations. These helices were found to be unstable relative to the corresponding “fully extended chain” conformation. The electric field of helices of 8–10 residues is about 20% stronger than that of models built fr...

We present a discrete solvent reaction field DRF model for the calculation of frequency-dependent hyperpolarizabilities of molecules in solution. In this model the solute is described using density functional theory DFT and the discrete solvent molecules are described with a classical polarizable model. The first hyperpolarizability is obtained in...

A discrete solvent reaction field model for calculating frequency-dependent molecular linear response properties of molecules in solution is presented. The model combines a time-dependent density functional theory QM description of the solute molecule with a classical MM description of the discrete solvent molecules. The classical solvent molecules...

In this work we present theory and implementation for a discrete reaction field model within Density Functional Theory DFT for studying solvent effects on molecules. The model combines a quantum mechanical QM description of the solute and a classical description of the solvent molecules MM. The solvent molecules are modeled by point charges represe...

In this paper a combined experimental and quantum chemical study of the geometry and opto-electronic properties of unsubstituted and dialkoxy-sustituted phenylene–vinylene oligomers (PV’s) is presented. The optical absorption spectra for PV cations with different chain lengths and substitution patterns were measured using pulse radiolysis with time...

Recently, it has become possible to measure the mobility of charges along isolated chains of conjugated polymers. The mobility of holes along poly(phenylenevinylene) and polythiophene backbones were reported to be 0.43 and 0.02 cm2 V-1 s-1, respectively. The large difference between the mobility of holes on poly(phenylenevinylene) and polythiophene...

In this work we have investigated the effects of substituting carbon atoms with B and N on the second hyperpolarizability of C60 using time-dependent density functional theory. We have calculated the second hyperpolarizability of the double substitute-doped fullerenes C58NN, C58BB and C58BN. For C60 only small changes in the second hyperpolarizabil...

Recently, it has become possible to measure the mobility of charges along isolated chains of conjugated polymers. The mobility of holes along poly(phenylenevinylene) and polythiophene backbones were reported to be 0.43 and 0.02 cm 2 V -1 s -1 , respectively. The large difference between the mobility of holes on poly-(phenylenevinylene) and polythio...

We present density-functional and time-dependent density-functional studies of the ground, ionic, and excited states of a series of oligomers of thiophene. We show that, for the physical properties, the most relevant highest occupied and lowest unoccupied molecular orbitals develop gradually from monomer molecular orbitals into occupied and unoccup...

A new charge analysis is presented that gives an accurate description of the electrostatic potential from the charge distribution in molecules. This is achieved in three steps: first, the total density is written as a sum of atomic densities; next, from these atomic densities a set of atomic multipoles is defined; finally, these atomic multipoles a...

Ab initio molecular orbital methods at the CBS-Q level of theory have been used to study the e€fect of substituent (F, Cl, NH2, OH and CH3) on the gas-phase acidities of formic acid, HCOOH, its silicon and sulphur derivatives R± M(ˆX)XH(MˆC, Si; X ˆO, S; R ˆF, Cl, OH, NH2 and CH3). For formic acid and its thio and dithio derivatives the acidity cha...

Ab initio molecular orbital calculations at the CBS-Q level of theory have been used to study the rotational conformers and acidity of dithiosilanoic acid and several of its derivatives R-SiSSH (R = H, F, Cl, NH2, OH and CH3). For all six acids studied the syn conformers are predicted to have the lowest energy. The syn-anti enthalpy difference vari...

The direct reaction field (DRF) model was developed for calculations of electronic properties of molecules in the condensed phase. In the DRF approach the electrons of (part(s) of a system is described with wavefunctions, the larger parts classically with point charges and polarizabilities. Leaving out the quantum-mechanical part(s) leads naturally...

The minimum energy conformations and racemization barriers for the chiral sterically overcrowded helical alkenes, trans- and cis-1,1',2,2',3,3',4,4'-octahydro-4,4'-biphenanthrylidenes (1 and 2), are reported. The trans-1 and cis-2 isomers can each adapt three different conformations, (P,P) and (M,M) (an enantiomeric pair) and an achiral (P,M) meso...

In the Direct Reaction Field (DRF) approach to the description of events in the condensed phase, quantum parts (QM) are embedded in a (semi-) classical environment (MM). QM is described with any appropriate wave function, while MM is modeled with point charges and interacting polarizabilities and/or a dielectric continuum, which may have finite ion...

The direct reaction field model was used to calculate the solvent shift of the n−π* transition of acetone in eight different solvents. The computed shifts correspond excellently to experimental values. We found that dispersion interactions are an essential part of the model for correctly describing the shifts in both polar and apolar solvents. Impr...

Reaction of pyridinyl-2-phosphonyl dichloride (6) with 1-phenyl-2,2-dimethylpropane-1,3-diol (9) leads to the two epimeric 2-oxo-2-(2-pyridinyl)-4-phenyl-5,5-dimethyl-1,3,2-dioxaphosphorinanes (10a,b). These can be separated and the stereochemistry assigned on the basis of 31P NMR spectroscopy. For 10a the pyridinyl substituent is arranged axially...

Femtosecond pump-probe spectroscopy is used to explore the excited-state dynamics of TPE in polar and nonpolar solvents. Four excited states are shown to play an important role: the vertically excited S1 state, the Franck-Condon relaxed S1 state, a twisted charge-resonance state (in the literature often referred to as biradical), and a charge-separ...

Thole's interacting polarizability model to calculate molecular polarizabilities from interacting atomic polarizabilities is reviewed and its major applications in computational chemistry are illustrated. The applications include prediction of molecular polarizabilities, use in classical expressions for intermolecular interactions for the computati...

Theo Thole's Ph.D. work was the basis for the Direct Reaction Field method for incorporating a semi-classical “solvent” in quantum chemical calculations. The early stages of his work and later progress is reviewed, and a typical example of his analytical and programming skills, so far unpublished, is given.

Sterically, the bis(N,O-bis(tert-butyl)(alkoxydimethylsilyl)amido) ligand-stabilized yttrium compounds [Me2Si(NCMe3)(OMe3)]2YR (R = BH4, O-2,6-(CMe3)2C6H3, N(SiMe3)2, CH(SiMe3)2) resemble the bis(pentamethylcyclopentadienyl) ligand set in Cp*2YR. Electronically, it is closer to the bis(benzamidinato) system in [PhC(NSiMe3)2]2YR, with negative charg...

The direct reaction field (DRF) force field gives a classical description of intermolecular interactions based on ab initio quantum-chemical descriptions of matter. The parameters of the DRF force field model molecular electrostatic and response properties, which are represented by distributed charges and dipole polarizabilities. The advantage of t...

The synthesis of [PhC(NSiMe3)2]2Y(μ-Cl)2Li·2THF (1) from YCl3·3.5THF and [PhC(NSiMe3)2]Li, which is easily transformed into [PhC(NSiMe3)2]2YCl·THF (2), provides a useful entry into the chemistry of several bis(N,N´-bis(trimethylsilyl)benzamidinato)yttrium complexes. Those prepared from 2 by chloride metathesis include [PhC(NSiMe3)2]2YR (R = BH4·THF...

The polarization behavior of the low lying excited states in the vicinity of the perpendicularly twisted (D2d) ethylene has been investigated in a quantum mechanical CISD approach, in which the quantum system was embedded in a polarized dielectric continuum modeling a non-symmetrical distribuion of the solvent around the solute. The results show a...

The solvent shift of the π* ← n transition of acetone in water, acetonitrile, and tetrachloromethane was calculated in a combined quantum mechanical—classical mechanical approach, using both dielectric continuum and explicit, polarizable molecular solvent models. The explicit modeling of solvent polarizability allows for a separate analysis of elec...

The solvent shift of the π* ← n transition of acetone in water, acetonitrile, and tetrachloromethane was calculated in a combined quantum mechanical-classical mechanical approach, using both dielectric continuum and explicit, polarizable molecular solvent models. The explicit modeling of solvent polarizability allows for a separate analysis of elec...

The embedding of a quantum mechanically described subsystem by classical representations of its surroundings is reviewed. The choices for a distributed monopole representation and a distributed (group) polarizability representation, as well as the continuum approach to model bulk effects, are discussed. Focus is on the practical implementation of t...

The dielectric constant of a material is a macroscopic property that measures the reduction of the electrostatic forces between charged plates separated by the material, compared to a vacuum as intermediate material. It is next encountered as a scaling parameter in Coulomb's law for interacting charges, not only in the force, but also in the energy...

The direct reaction field (DRF) approach is a practical method for incorporating environmental (e.g. solvation) effects on a system of which the electronic charge distribution is described by wave functions, and the “solvent” is modelled by a collection of interacting point charges and (point) polarizabilities. The DRF method is briefly summarized....

The tautomer equilibrium of a number of 4-substituted imidazoles in the gas phase and in aqueous solution was calculated by combining quantum chemical ab initio calculations on the tautomers in the gas phase with classical electrostatics calculations (a continuum model and a Monte Carlo method with a limited number of discrete solvent molecules) to...

The effects of the solvent on the stability of the zwitterion in the active site of papain is investigated with numerical methods. The solvent is represented by a homogeneous dielectric continuum surrounding a cavity, defined by a fragment of the protein enclosed by a surface obtained following Connolly's method. The discretisized boundary surface...

The direct reaction field (DRF) method, developed to incorporate the effects of a (large) semiclassical environment into the Hamiltonian of a quantum mechanical system, is briefly reviewed. It is shown that the DRF method behaves—at least—like a supermolecule SCF calculation. With the water dimer as an example, the similarity with the SCF procedure...

The proton transfer between the Cys25 and His159 residues in the active centre of the proteolytic enzyme papain is investigated with the Hartree-Fock SCF direct reaction field method. The active centre is treated quantum mechanically, while the environment is represented by interacting partial charges and polarizabilities. All protein atoms around...

A molecular model for electronic polarization of water is defined, consisting of interacting point dipole polarizabilities in an electric field generated by atomic point charges, which represent the gasphase dipole moment of water molecules. The induced dipole equations are solved self consistently. The model has been implemented in a Monte Carlo h...

We present a simple model to deal with long range electrostatic interactions in computer simulations of solvated molecules and ions. The model combines a discrete molecular description of the first two or three solvation layers with a continuum description of the bulk solvent. The solute is described quantum mechanically. For a series of amines goo...

A "double zeta" basis set ab initio method was used for investigation of the systems (trimethylamine-dimethylphosphate monoanion)H+, aniline-dimethylphosphate monoanion and formanilide-dimethylphosphate monoanion, which represent the models for associative sites of both local anaesthetics and the phospholipid part of the nerve membrane. According t...

In this paper the relevance of ab initio quantum mechanical calculations is briefly reviewed. A method to extend such calculations to the domain of solvent effects and the theoretical investigation of chemical reactions in the active site of a protein is discussed.

Recently, it was suggested that parallel β-sheets have a significant dipole moment, in contrast to antiparallel sheets. Ab initio molecular-orbital (MO) calculations on parallel and antiparallel β-strands of tetra(Gly) show that they have very similar charge distributions. Interaction energies between two and three strands of tetra(Gly), obtained u...

The quantum-chemical PCILO method has been used to perform a conformational analysis of the 1-[2-(2-methoxyphenylcarbamoyloxy)ethyl]piperidine (B) and its cation (BH⊕) which belong to a group of phenylcarbamates with considerable local anesthetic activity. For B the most stable conformation has a gauche arrangement of the O-C-C-N fragment. For BH⊕...

A minimal basis set ab initio SCF MO method has been used to find the stable conformations of the polar COO, NHCO and NHCOO groups in the methyl ester of 4-aminobenzoic acid (I), 2,6-dimethylacetanilide (II) and the methyl ester of 2-methoxyphenylcarbamic acid (III) which are models for the local anesthetics procaine, lidocaine and heptacai...

A "double zeta" basis set ab initio SCF MO method has been used to study intermol-ecular hydrogen bonding in the systems [trimethylamine-dimethylphosphate monoanion] -H' (I), anilinedimethylphosphate monoanion (II) and formanilide-dimethylphosphate monoanion (III) which represent the models for associative sites of both local anesthetics and the ph...

The feasibility of the inclusion of reaction field effects in accurate ab initio self-consistent field-molecular orbital calculations was studied in the case of proton transfer in the active site of actinidin. The effects of the polarizability of the environment were included, using the direct reaction field model, which treats the environment as a...

A new and efficient method is proposed for obtaining atomic charges from molecular wave functions, preserving both total charge and dipole moment. The method is independent of the type of wave function (SCF, CI) and does not refer explicitly to the basis set used, nor to integral approximations (e.g. CNDO) applied. The method takes very little time...

Ab initio molecular orbital methods are used to study local anesthetics of the ester, analide and carbamate types. Electrostatic molecular potential contour maps were evaluated for aromatic parts of those type of drugs. Because the main constituents of cell membranes are lipids and proteins, our further SCF MO studies concerned interaction of polar...

The induction and dispersion terms obtained from quantum-mechanical calculations with a direct reaction field hamiltonian are compared to second order perturbation theory expressions. The dispersion term is shown to give an upper bound which is a generalization of Alexander's upper bound. The model is illustrated by a calculation on the interaction...

Some problems concerning the reaction mechanisms of papain and thiolsubtilisin are discussed. Results of ab initio SCF calculations, which contributed to the solution of those problems, are briefly reviewed. It is concluded that the environment of an enzyme’s active site plays an important part in the activity.

Minimal basis set ab initio SCF MO expectation values of the electrostatic potential of an octa-alanine α-helix are reported. The energy profile for a proton moving through the interior of the helix is given. It is suggested that the internal electric field of a helix may be essential in biological ion pumps.

Structured macromolecules such as proteins have intramolecular electric fields of considerable strength. Sources of such fields may be ionizable groups, but also the protein backbone contributes, particularly when α-helices are present. The fields cause shifts in the physico-chemical properties of, e.g., active site residues of enzymes, which may c...

Based on computed proton affinities for several model systems, the energetics of proton transfer and the acidity of the catalytic triads Cys-His-Asn (papain). Cys-His-Asp (thiol-subtilisin) and Ser-His-Asp (subtilisin) are discussed. It is shown that in papain the ion-pair Cys--HisH+ exists owing to the intramolecular electric field, and that a sim...

Based on computed proton affinities for several model systems, the energetics of proton transfer and the acidity of the catalytic triads Cys-His-Asn (papain). Cys-His-Asp (thiol-subtilisin) and Ser-His-Asp (subtilisin) are discussed. It is shown that in papain the ion-pair Cys−-HisH+ exists owing to the intramolecular electric field, and that a sim...

A new formalism is proposed for incorporating solvent effects into the quantum mechanical description of molecular electronic states. In contrast to existing methods, it does not lead to a non-linear effective hamiltonian, while both the solvent/solvent and the solute/solvent interactions are treated self-consistently. It also accounts more accurat...

Ab initioMO calculations, using both minimal (STO-3G) and extended (Roos–Siegbahn) basis sets are reported for the systems methanethiol–imidazole, methanethiol–imidazole–formaldehyde, and methanethiol–imidazole–formamide, which, together with a point-change representation of a long -helix, form models for the active site of papain. It is shown that...

On the system methanethiol/imidazole/formaldehyde (modelling the active site of papain) we performed ab initio self-consistent-field molecular orbital calculations using a rather large basis of Gaussian-type functions. A point charge representation of the long central alpha-helix present in the enzyme, was added in order to establish the influence...

Phosphate moieties bind frequently at N-termini of helices in proteins. It is shown that this corresponds with an optimal interaction of the helix dipole and the charged phosphate. This favourable arrangement may have been discovered several times during evolution. In some enzymes, the helix dipole might be used in catalysis.

Ab initio self-consistent-field molecular-orbital calculations were performed on octahedral FeF6 and Fe(CN)6 clusters using extensive basis sets of Gaussian-type functions. Two distances relevant for ferrous and ferric compounds are considered. In this paper, we report the part of our results that is relevant for a determination of the isomer-shift...

Ab initio molecular orbital calcuiations using a contracted basis of gaussian orbitals on the system methanethiol/imidazole are reported. For the hydrogen bond S---H---N in this system, which was chosen as a model for the active site of papain, a double-well potential was found at a S-N separation of 3.35 Å. This sustains a newly proposed mechanism...

Die unterschiedliche Reaktivität der Diene (I) und (II) bei Diels-Alder-Reaktionen mit Tetracyanäthylen wird diskutiert und mit zahlreichen ähnlichen Verbindungen wie (III) und (IV) verglichen.

A method is given for obtaining the common molecular integrals over generalized gaussian functions: The present algorithms are expected to be more efficient than those given in earlier work by the same author.

A method for the evaluation of molecular integrals over generalised gaussian functions is given.

The use of ellipsoidal gaussian type orbitals in ab initio calculations on molecular systems of small and intermediate size is demonstrated, in both non-linear and SCF MO schemes. The method is an extension of Frost's Floating Gaussian Orbital Method. Results for conformational properties (barriers to internal rotation in ethane and 1,3-butadiene)...

A discrete solvent reaction field model for calculating molecular linear response properties in solution" J. Chem. Phys. 119, 3800-3809, 2003. 9.1 Abstract A Discrete Solvent Reaction Field model for calculating frequency-dependent molecular linear response properties of molecules in solution is presented. The model combines a Time-Dependent Densit...