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We investigate the role of excitonic coupling between retinal chromophores of Krokinobacter eikastus rhodopsin 2 (KR2) in the circular dichroism (CD) spectrum using an exciton model combined with the transition density fragment interaction (TDFI) method. Although the multimer formation of retinal protein commonly induces biphasic negative and positive CD bands, the KR2 pentamer shows only a single positive CD band. The TDFI calculation reveals the dominant contribution of the Coulomb interaction and negligible contributions of exchange and charge-transfer interactions to the excitonic coupling energy. The exciton model with TDFI successfully reproduces the main features of the experimental absorption and CD spectra of KR2, which allow us to investigate the mechanism of the CD spectral shape observed in the KR2 pentamer. The results clearly show that the red shift of the CD band is attributed to the excitonic coupling between retinal chromophores. Further analysis reveals that the weak excitonic coupling plays a crucial role in the shape of the CD spectrum. The present approach provides a basis for understanding the origin of the KR2 CD spectrum and is useful for analyzing the mechanism of chromophore–chromophore interactions in biological systems., ファイル公開：2021/07/28

An extensive study of structures and energetics for anionic pentamer and hexamer clusters is performed employing high level ab initio quantum chemical methods, such as the density-fitted orbital-optimized linearized coupled-cluster doubles (DF-OLCCD), coupled-cluster singles and doubles (CCSD), and coupled-cluster singles and doubles with perturbative triples [CCSD(T)] methods. In this study, sixteen anionic pentamer clusters and eighteen anionic hexamer clusters are reported. Relative, binding, and vertical detachment energies (VDE) are presented at the complete basis set limit (CBS), extrapolating energies of aug4-cc-pVTZ and aug4-cc-pVQZ custom basis sets. The largest VDE values obtained at the CCSD(T)/CBS level are 9.9 and 11.2 kcal mol-1 for pentamers and hexamers, respectively, which are in very good agreement with the experimental values of 9.5 and 11.1 kcal mol-1. Our binding energy results, at the CCSD(T)/CBS level, indicate strong bindings in anionic clusters due to hydrogen bond interactions. The average binding energy per water molecules is -5.0 and -5.3 kcal mol-1 for pentamers and hexamers, respectively. Furthermore, our results demonstrate that the DF-OLCCD method approaches to the CCSD(T) quality for anionic clusters. The inexpensive analytic gradients of DF-OLCCD compared to CCSD or CCSD(T) make it very attractive for high-accuracy studies.

A reduced-dimensional effective-mode representation is developed in order to efficiently describe excited-state dynamics of multichromophoric donor-acceptor aggregates within a linear vibronic coupling model. Specifically, we consider systems where vibrational modes pertaining to a given molecular fragment couple both to local excitations of Frenkel type and delocalized states of charge transfer exciton type. A hierarchical chain representation is constructed which is suitable to describe correlated fluctuations, leading to a set of correlated spectral densities. An application is shown for a first-principles parameterized model of an oligothiophene H-type aggregate whose properties are modified due to the presence of charge transfer excitons. Within a pentamer model comprising 13 electronic states and 195 normal modes, good convergence of the effective-mode representation of the spectral densities is achieved at the eighth order of the hierarchy with 104 modes, and a qualitatively correct picture is obtained at the sixth order with 78 modes.

The adsorption kinetics of water on Ru(001) was simulated using molecular dynamics (MD) and equilibrium-model approach. The results nicely reproduce observations from STM imaging, work function change, and IR measurements. The agreement with experimental results is based on the formation of stable clusters already at very low surface coverage and temperature. Tetramers are predicted to be relatively stable compared to smaller and larger clusters. The dipole moment per water molecule continuously decreases from 2.2D for the monomer down to 1.1D for pentamer and larger clusters. Dimers are found to diffuse faster than monomers or larger clusters, with activation energy for diffusion of 2.9 kcal/mol, in agreement with recent STM measurements. A unique mechanism for dimers diffusion is proposed. Temperature programmed desorption (TPD) spectra from a metal surface were calculated by employing the MD scheme. These spectra were found identical to the standard Redhead line-shape analysis of the experimental TPD s...

Various computational ab-initio methods are employed to study the doubly-charged carbon system C52+. For its electronic ground state, equilibrium geometries are identified, and their stability against dissociation investigated. Multireference configuration-interaction results indicate a weakly bound but thermochemically stable dication.

Although various low-lying energy structures of electron–water clusters, e−–(H2O)2–6, have been reported, some of the global minimum energy structures (in particular, for the tetramer and pentamer) are still not clearly characterized yet. Therefore, using high-level ab initio calculations, we have investigated several new low-lying energy conformers in addition to previously reported ones. The lowest energy conformer for the pentamer is found to have a wedge-like structure which has never been studied before. Based on the experimental vertical electron-detachment energies and OH vibrational spectra of the electron–water clusters, we report the most probable structures and their nearly isoenergetic structures. The OH vibrational frequencies of e−(H2O)2–6 and e−HOD(D2O)1–5 are investigated, and are found to be in excellent agreement with the available experimental data. Their O–H stretch frequency shifts are classified in terms of the types of water molecules.

Molecular dynamics simulations of water pentamers were carried out using the semiempirical Parameterization Method 3 method to calculate the forces. Simulations were performed in the microcanonical ensemble, at several (average) vibrational temperatures. Three distinct transitions were observed in these systems, corresponding to the onset of phase coexistence and of two hydrogen bond rearrangements that were predicted by previous structural calculations. A detailed study of the high-temperature pentamer dynamics is presented, which clarifies the distinction between liquidlike behavior and simple structural rearrangements in these systems.

Various structures of halide-water pentamers and hexamers have been investigated using extensive ab initio calculations. Then, we compare the structures, spectra, and electronic properties of the hydrated fluoride, chloride, bromide, and iodide systems. Although some of the fluoride and iodide systems have been investigated earlier, we have carried out more accurate calculations on an enlarged conformational ensemble. The chloride-, bromide-, and iodide-water pentamers and hexamers behave somewhat similarly, but differently from the fluoride-water pentamer and hexamer. Fluoride-water clusters show semisurface (or semi-internal) structures, while chloride-, bromide-, and iodide-water clusters show surface structures. We substantiate our findings by evaluating various electronic properties such as ionization potentials, natural bond orbital charges, dipole moments, and charge-transfer-to-solvent energies, as well as vibrational frequencies of the low-energy halide-water pentamers and hexamers.

Theoretical studies of hydrogen bond network rearrangement (HBNR) dynamics in liquid water have indicated that librational motions initiate the hydrogen bond breaking/formation processes. We present the results of using a simple time evolution method to extract and compare the tunneling lifetimes for motions that break and reform the hydrogen bond for the water dimer, trimer, and pentamer from the experimentally measured tunneling splittings in the ground and excited intermolecular vibrational states. We find that the specific nature of the intermolecular vibrational excitation does not significantly influence the tunneling lifetime of the dimer, but that only excitations to a librational vibration affect the water trimer and pentamer lifetimes. The specific enhancement of bifurcation tunneling in larger clusters relative to the dimer also indicates that hydrogen bond cooperativity is a vital element of these dynamics.

Hydrogen bonds in solid and liquid water are formed and broken via librational vibrations, hence characterizing the details of these motions is vital to understanding these important dynamics. Here we report the measurement and assignment of 875 transitions comprising 6 subbands originating from out-of-plane librational transitions of the water pentamer-d10 near 512 cm-1. The precisely measured (ca. 1 ppm) transitions reveal bifurcation splittings of ∼1884 MHz, a ∼4000× enhancement over ground state splittings and 100× greater than predicted by theory. The pentamer is thus the third water cluster to display greatly enhanced bifurcation tunneling upon single quantum excitation of librational vibrations. From the intensity pattern of the observed transitions, the mechanism of bifurcation is established by comparison with theoretical predictions.

Ab initio calculations have been carried out to study the water clusters of undecamer [(H2O)11] and dodecamer [(H2O)12]. At the level of Moller–Plesset second-order perturbation theory using TZ2P++ basis set, the lowest-energy conformer of the undecamer has the skeletal structure of Prism56 that a cyclic pentamer and a cyclic hexamer are fused into a prism shape with 16 hydrogen bonds (HBs). In this case, there are quite a number of nearly isoenergetic conformers with different hydrogen orientations. Among these, more stable conformers tend to have dangling H atoms separated (i.e., less clustered). The lowest energy conformer of the undecamer is different in hydrogen orientation from any previously suggested structure (including the ones obtained from various minimization algorithms). A second lowest energy skeletal structure is of Prism56B that a cyclic pentamer and an open-book hexamer are fused into a prism shape with 17 HBs. The most stable dodecamer is a fused cubic or tetragonal prism skeletal struc...

Optimized structures and bonding energies have been calculated for ammonia clusters from n=3 to n=18 using a pairwise additive model potential. The trimer and tetramer are stable cyclic configurations. From the pentamer onward the structures are three dimensional with an increasing tendency to amorphous behavior. The exceptions are the heptamer with a Cs axis, the hexadecamer with a central atom, and the very stable and completely symmetric dodecamer with the D6h point group. Here each ammonia molecule is bound by two covalent and two hydrogen bonds. In general, the coordination number increases from 2.0 for the rings over 4.0 for n=12 to 4.2 for n=18. The structures agree where available with previously obtained results for a more elaborate potential.

Geometries and energy separations of the various low-lying electronic states of Pt5 with different structural arrangements have been investigated. The complete active space multiconfiguration self-consistent-field (CASMCSCF) method followed by large-scale multiconfiguration singles plus doubles configuration interaction (MRSDCI) that included up to 1.64 million configuration spin functions have been used to compute several electronic states. A 1B2 (C2v) electronic state of a distorted tetragonal pyramid equilibrium structure was found to be the minimum energy geometry. We also compared our MRSDCI results with density functional as well as Mo/ller-Plesset second-order perturbation calculations. The dissociation and atomization energies have been computed and the results, together with our previous findings for the smaller Ptn (n=2–4) clusters, were compared with other group 10 member clusters viz., Nin (n=2–5) and Pdn (n=2–5) and the experimental findings.

Conformers of water anionic pentamer cluster (H2O)5− have been reported here in using ab initio as well as density functional methods. Relative stabilities of these conformers obtained from inclusion of electron correlation at various levels indicate that they are very close in energies. The plots of singly occupied molecular orbital (SOMO) reveal that the excess electron exhibits stabilization selectively as either a surface state or an internal state. Vibrational frequencies of some of the conformers have also been reported at the MP2 level.

Photofragment angular and final rotational state distributions have been measured, corresponding to the vibrational predissociation of HF polymers [(HF)N N=5–7]. The present experiments confirm the theoretical prediction that, for clusters in this size range, the only open dissociation channel corresponds to the “evaporation” of a single HF monomer. The pump–probe experiments reported here indicate that the resulting HF monomer is produced with only modest rotational excitation. Rotational temperatures of 180 and 140 K have been determined for the evaporated HF monomer following dissociation of the HF pentamer and hexamer, respectively. Energy conservation in these photodissociation studies provides upper limits for the dissociation energies (D0), namely, 2941 cm−1 and 2854 cm−1 for the pentamer and hexamer, respectively.

We theoretically investigated collision cross sections due to the attractive forces between NH4+(NH3)n−1 (n=2–8) and ND3. We found that the dependence of the collision cross sections on collision energy and cluster size are comparable to those of measured fusion cross sections. The kinetic magic number, n=5, is related to the structure of the pentamer. Namely, the center ion in the pentamer is surrounded by first-shell ammonia molecules.

We have studied the electronic structures, energetics, electron vertical detachment energies (VDEs), and O–H vibrational spectra of various conformers of water clusters with an excess electron [e+(H2O)n, n=2–5] or anionic water clusters [(H2O)n−] using comprehensive ab initio calculations. As noted in our preliminary work [J. Kim et al., Phys. Rev. A 59, 930 (1999)], the structure of the water dimer anion is characterized to be linear-like (slightly towards the cis conformer) but very floppy with large wide-ranging zero point vibration motion at 0 K. The lowest energy structures of the water trimer to pentamer anion are all cyclic with very small VDEs (< 0.05 eV). However, these cyclic structures which are metastable are prone to become the neutral species by releasing an excess electron because the transition barriers seem to be very small. Thus, observation of such cyclic structures would not be feasible. On the other hand, a linear water trimer structure which is 0.8 kcal/mol higher in energy than the ...

The intermolecular potential energy surface and the torsional-puckering (TP) motion of the cyclic homodromic water pentamer were theoretically investigated at the level of second-order Moller–Plesset perturbation theory using double- and triple-zeta correlation-consistent basis sets including diffuse functions. Extensive searches yielded three cyclic homodromic stationary points: (i) the puckered global minimum structure GS, (ii) a torsional-puckering saddle point, 62 cm−1 higher, denoted TS1, and (iii) a planar C5h symmetric structure (Hessian index 7), 800 cm−1 higher in energy. Harmonic vibrational frequencies and normal modes were calculated for all stationary points. Based on the energies and second derivatives of the GS and TS1 structures a cyclic minimum energy path for the large-amplitude TP motion with ten permutationally equivalent minima was constructed. The ground and all excited states are delocalized by TP pseudorotation, giving vibrationally averaged C5h symmetry. The first pseudorotational...

The Raman spectrum of Ag5, mass-selected from a sputtered jet of silver cluster ions, neutralized and matrix isolated in solid argon, is reported. Analysis of the frequencies and intensities of the 7 vibrational modes recorded suggests unequivocally that the molecule has a planar trapezoidal structure. No other reasonable structure is consistent with the observations. Nor is there evidence for more that one structure coexisting with the planar trapezoid. The observation is in accord with the conclusions of most quantum computations on Ag5. The silver pentamer is found to photofragment into the dimer and trimer when irradiated with 458 or 466 nm laser light.

Geometry optimizations, rearrangement mechanisms, spectral intensities, and tunneling splittings are reported for the water pentamer. Two low energy degenerate rearrangements are identified for the chiral cyclic global minimum which are analogous to processes that lead to observable tunneling splittings in the water trimer. Fourteen different pathways are characterized by ab initio calculations employing basis sets up to double‐zeta plus polarization (DZP) quality with subsequent reoptimization of the associated minima using the Becke exchange and the Lee–Yang–Parr correlation functionals (BLYP) with the same basis. All the pathways have been recomputed for a number of different empirical potentials, some of which reproduce the two lowest energy degenerate rearrangements quite well. However, none of the empirical potentials support all the higher energy ab initio minima. Qualitative estimates of the two tunneling splittings associated with the lowest energy pathways suggest that at least one might be observable experimentally; the associated splitting patterns and nuclear spin weights are also reported. The corresponding stationary points were finally reoptimized using DZP basis sets plus diffuse functions with the BLYP exchange‐correlation functional.

High-level quantum-chemical ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute the vertical and adiabatic ionization potentials of several water clusters: dimer, trimer, tetramer, pentamer, hexamer book, hexamer ring, hexamer cage, and hexamer prism. The present results establish reference values at a level not reported before for these systems, calibrating different computational strategies and helping to discard less reliable theoretical and experimental data. The systematic study with the increasing size of the water cluster allows obtaining some clues on the structure and reductive properties of liquid water.

We present the results of mass‐selective, ionization‐detected stimulated Raman spectroscopies on jet‐cooled benzene clusters from the trimer to the octamer. The data pertain to the fundamentals of the totally symmetric ring‐breathing (ν1) and C–H stretch (ν2) modes of benzene and provide information about geometrical structure and vibrational dynamics. For the trimer, the results indicate a species in which all three benzenes reside in equivalent sites. For the higher clusters the results point to geometries involving two or more inequivalent sites. The ν1‐excited trimer is found to decay on a nanosecond, or longer, time scale. The ν2‐excited trimer decays on a time scale of greater than 5 ps. Similar timescales characterize the decays of the ν2‐excited tetramer and pentamer.

The minimum energy structures and the classical dynamics of (H2O)n clusters, with n=3–6,8, have been investigated with the potential function of Cieplak, Kollman, and Lybrand. The potential is the sum of a pairwise additive part plus a polarization term calculated iteratively from the permanent and induced dipole moments. It is found that at the minimum energy structures the polarization energy makes a contribution of about 13% in the total energy. Caloric curves and rms fluctuations of the oxygen–oxygen bond lengths show that the tetramer, with a tetragonal minimum geometry, and the octamer, with a cubic minimum geometry, are more stable clusters than the pentamer and hexamer. The geometries of absolute minima for the trimer, tetramer, and octamer agree with those predicted by other potentials. For the pentamer and hexamer the present potential predicts floppy type structures instead of cyclic ones, which are supported by other functions and ab initio calculations. The dynamics of water clusters is chaot...

A computational study predicts a number of stable, unusual halogen- and hydrogen-bonded complexes involving FBr, NCH, and FH. Starting from the linear halogen-bonded FBr...NCH dimer, increasingly more stable complexes are obtained by the successive hydrogen bonding of one to three FH molecules to the lone pairs on the Br atom of FBr to form a trimer, tetramer, and pentamer. A hexamer is obtained from the pentamer by the bonding of FH to the F atom of FBr. The combined halogen and hydrogen bonding gives rise to a large computed zero-point corrected binding energy of 98 kJ/mol for the hexamer at the MP2/6-31++G(d,p) level of theory.

The chemistry and kinetics of size‐selected Co+n cluster‐ion (n=2–8) reactions with CO are studied using a selected ion drift tube affixed with a laser vaporization source operated under well‐defined thermal conditions. All reactions studied in the present work are found to be association reactions. Their absolute rate constants, which are determined quantitatively, are found to have a strong dependence on cluster size. Similar to the cases of reactions with many other reactants such as H2 and CH4, Co+4 and Co+5 display a higher reactivity toward the CO molecule than do clusters of neighboring size. The multiple‐collision conditions employed in the present work have enabled a determination of the maximum coordination number of CO molecules bound onto each Co+n cluster. It is found that the tetramer tends to bond 12 CO molecules, the pentamer 14 CO, hexamer 16 CO, and so on. The results are interpreted in terms of Lauher’s calculation and the polyhedral skeletal electron pair theory. All the measured maximum coordination numbers correlate extremely well with the predictions of these theories, except for the trimer where the measured number is one CO less than the predicted value. The good agreement between experiment and theory enables one to gain some insight into the geometric structure of the clusters. Based on the present findings, the cobalt tetramer cation is interpreted to have a tetrahedral structure, the pentamer a trigonal bipyramid, and the hexamer an octahedral structure. Other cluster structures are also discussed.

X-ray absorption spectra have been determined for ethylene and free base phthalocyanine at the carbon K-edge with use of the complex polarization propagator method combined with Kohn-Sham density functional theory and the Coulomb attenuated method B3LYP exchange-correlation functional. Apart from isolated molecules, the study includes pi-stacked systems of the phthalocyanine dimer and the ethylene dimer, trimer, tetramer, and pentamer. For ethylene, pi-stacking involves a reduction in transition energy of the valence pi( *)-band by some 70 meV and large spectral changes (regarding also shape and intensity) of the Rydberg bands. For phthalocyanine, there are large spectral changes in the entire valence pi( *)-part of the spectrum.

We investigate the quantum thermodynamic properties of small (HCl)(n) clusters using stereographic projection path integral simulations. The HCl stretches are rigid, the orientations are mapped with stereographic projection coordinates, and we make use of the reweighted random series techniques to obtain cubic convergence with respect to the number of path coefficients. Path integral simulations are converged at and above 10 K for the pentamer and above 15 K for the dimer and the trimer. None of the systems display a melting feature in the classical limit. We find an evidence of quantum induced melting between 15 and 45 K.

Size‐selective infrared photodissociation spectra of (CH3OH)n clusters from n=2 to n=9 were measured near the absorption band of the C–O stretching mode of the monomer at 1033.5 cm−1 . The experiments were carried out in a molecular‐beam apparatus in which the clusters are generated in a supersonic expansion and afterwards size selected in a scattering experiment with helium atoms. The internally excited clusters are dissociated by the radiation of a cw CO2 laser in a new antiparallel arrangement of the scattered cluster beam and laser beam. The observed spectra vary from the dimer, for which a double‐peak structure appears, to the single‐peak spectra of the trimer, tetramer, and pentamer which are continuously shifted to higher frequencies. A special transition is seen from the pentamer to the hexamer, for which again a double‐peak structure is observed which continues to larger clusters. Applying an intermolecular model potential, a correlation between the observed spectra and the cluster configuration ...

We report MP2 and Coupled Cluster Singles, Doubles, and perturbative Triples [CCSD(T)] binding energies with basis sets up to pentuple zeta quality for the (H2O)m=2-6,8 water clusters. Our best CCSD(T)/Complete Basis Set (CBS) estimates are -4.99 ± 0.04 kcal/mol (dimer), -15.8 ± 0.1 kcal/mol (trimer), -27.4 ± 0.1 kcal/mol (tetramer), -35.9 ± 0.3 kcal/mol (pentamer), -46.2 ± 0.3 kcal/mol (prism hexamer), -45.9 ± 0.3 kcal/mol (cage hexamer), -45.4 ± 0.3 kcal/mol (book hexamer), -44.3 ± 0.3 kcal/mol (ring hexamer), -73.0 ± 0.5 kcal/mol (D2d octamer), and -72.9 ± 0.5 kcal/mol (S4 octamer). We have found that the percentage of both the uncorrected (De) and basis set superposition error-corrected (De (CP)) binding energies recovered with respect to the CBS limit falls into a narrow range on either sides of the CBS limit for each basis set for all clusters. In addition, this range decreases upon increasing the basis set. Relatively accurate estimates (within

We extend the active space decomposition method, recently developed by us, to more than two active sites using the density matrix renormalization group algorithm. The fragment wave functions are described by complete or restricted active-space wave functions. Numerical results are shown on a benzene pentamer and a perylene diimide trimer. It is found that the truncation errors in our method decrease almost exponentially with respect to the number of renormalization states M, allowing for numerically exact calculations (to a few microhartrees or less) with M = 128 in both cases. This rapid convergence is because the renormalization steps are used only for the interfragment electron correlation.

With a view toward a better understanding of changes in the peak position and shape of the first absorption band of water with condensation or temperature, results from electronic structure calculations using high level wavefunction based and time-dependent density functional methods are reported for water pentamers. Excitation energies, oscillator strengths, and redistributions of electron density are determined for the quasitetrahedral water pentamer in its C(2v) equilibrium geometry and for many pentamer configurations sampled from molecular simulation of liquid water. Excitations associated with surface molecules are removed in order to focus on those states associated with the central molecule, which are the most representative of the liquid environment. The effect of hydrogen bonding on the lowest excited state associated with the central molecule is studied by adding acceptor or donor hydrogen bonds to tetramer and trimer substructures of the C(2v) pentamer, and by sampling liquid-like configurations having increasing number of acceptor or donor hydrogen bonds of the central molecule. Our results provide clear evidence that the blueshift of excitation energies upon condensation is essentially determined by acceptor hydrogen bonds, and the magnitudes of these shifts are determined by the number of such, whereas donor hydrogen bonds do not induce significant shifts in excitation energies. This qualitatively different role of donor and acceptor hydrogen bonds is understood in terms of the different roles of the 1b(1) monomer molecular orbitals, which establishes an intimate connection between the valence hole and excitation energy shifts. Since the valence hole of the lowest excitation associated with the central molecule is found to be well localized in all liquid-like hydrogen bonding environments, with an average radius of gyration of ~1.6 Å that is much lower than the nearest neighbor O-O distance, a clear and unambiguous connection between hydrogen bonding environments and excitation energy shifts can be established. Based on these results, it is concluded that peak position of the first absorption band is mainly determined by the relative distribution of single and double acceptor hydrogen bonding environments, whereas the shape of the first absorption band is mainly determined by the relative distribution of acceptor and broken acceptor hydrogen bonding environments. The temperature dependence of the peak position and shape of the first absorption band can be readily understood in terms of changes to these relative populations.

We present extensions to the local-monomer (LMon) Model, a general quantum method to describe coupled intramolecular vibrational modes of a molecular cluster consisting of a set of monomers [Y. Wang and J. M. Bowman, J. Chem. Phys. 134, 154510 (2011)], to incorporate monomer-monomer coupling. A central aspect of the LMon model is a local normal-mode analysis, done for each monomer, perturbed by all other mononers. Monomer-monomer coupling is described by several approaches based on these normal-mode analyses. Two are Hückel-type models, where coupling constants for each intramolecular mode are determined non-empirically from normal-mode analyses. One model, the simple one, is limited to nearest-neighbor interactions. The second and more general one determines monomer-monomer couplings from the full and local-monomer Hessians, with no further assumptions. The simple approach is applied to the water tetramer, pentamer and ring hexamer. For the tetramer and ring hexamer cases, artificial degeneracies of the intramolecular energies in the LMon model, owing to the high symmetry of the cluster, are correctly lifted. The general approach to obtain coupling constants is illustrated for the ring hexamer, where new fundamental energies are reported. Other, more rigorous approaches are suggested but not implemented.

The first theoretical study on static polarizability and polarizability anisotropy of small nickel clusters up to the pentamer is presented. All-electron-type calculations were performed using a finite field approach as implemented in the density functional program deMon2K. A newly developed first-order field-induced basis set for density functional calculations was employed. For the static polarizability per atom of these clusters, a different trend to the one reported in the literature for other transition metal cluster systems of similar size, is observed.

Ab initio self‐consistent field calculations with STO‐3, 4‐31, and 6‐31G basis sets are performed on methyllithium monomer dimer, trimer, and pentamer. The calculations provide data on binding energies and optimum geometries of various structures as well as indicate the formation of a lithium bond (between tetramers) similar to hydrogen bonds. Several tetrameric structures were investigated including one of D2d symmetry (resembling the ethyllithium tetramer) which is of possible importance in lithium exchange reactions.

Many‐body contributions to the energies, forces, electron densities, dipole moments, and Mulliken charges for a water molecule bound in a tetrahedral environment have been calculated by ab initio SCF methods. An (H2O)5 and two ⊕2+2⋅H2O complexes have been investigated. Nonadditive effects in the energies can to a large part be explained on the basis of the electron redistribution for interacting pairs, while nonadditive effects in the electron rearrangement were found to be small. Four‐ and five‐body corrections to all the pentamer properties calculated were found to be small.