Potential energy surfaces for the interaction of hydrogen atoms with beryllium metal clusters

With a modified CNDO/2 molecular orbital approach, potential energy surfaces are computed for the attack of beryllium atom clusters simulating “smooth” (0001) and “corrugated” (1010) faces of beryllium metal. Several stable sites for chemisorption are found with binding energies of 40–55 kcal/mole, but penetration of the lattice appears possible at some points. Results are compared with the preliminary ab initio predictions of Bauschlicher, Liskow, Bender and Schaefer.     

Potential energy surfaces of OsCO

Potential energy surfaces for the low-lying states of osmium carbon monoxide (OsCO) have been studied using the complete active space multi-configuration self-consistent field (CAS-MCSCF) followed by multireference singles+doubles configuration interaction (MRSDCI). Additionally, spin–orbit effects were included through the relativistic configuration interaction method. It is found that the ground state of OsCO is an 0⁺ spin–orbit state which is a mixture of ³Σ⁻ and ¹Σ⁺. Spin–orbit coupling not only splits the various electronic states of OsCO but also mixes different electronic states.     

Potential energy surfaces for the interaction of atomic and diatomic hydrogen with lithium metal clusters

In this paper a modified CNDO/2 method is used to study the interaction of hydrogen atoms and molecules with molecular clusters simulating the (100) surface of solid lithium metal. The modification, described in an earlier papers, involves rescaling bicentric CNDO/2 energy contributions with known diatomic bond energies. Potential energy curves are calculated for six attack points by the hydrogen atom on the surface, and for one attack point by the molecule. The results indicate that in both atom and molecule forms hydrogen penetrates the surface and that the molecule most likely dissociates.     

Potential energy surfaces of carbon dioxide

Several bent valence states of CO₂ are characterized by means of full-valence-space MCSCF calculations. The ground state potential energy surface exhibits a double well corresponding to a ring minimum, with C_2vsymmetry (¹A₁) and a 73.1° OCO angle, in addition to the linear (¹σ) global minimum. The transition state for the ring opening process, which has a barrier of 12.1 kcal/mole with respect to the ring minimum, is however found to have C_s symmetry. Double minima are also shown to exist for the ¹A₂, ¹B₁ and ¹B₂ excited states. However, in these cases all minima are bent. Cross sections through the ground state potential energy surface corresponding to the two collinear exchange reactions O(¹D) + CO(¹σ⁺) → OC(¹σ⁺) + O(¹D) C(³P) + O₂(³σ) → CO(¹σ⁺) + O(¹D) are also calculated and their energy contour maps are reported. The latter reveals the existence of a stable linear intermediate with the structure COO. © 1994 John Wiley & Sons, Inc.     

Potential energy surfaces for gas-surface reactions

A method for constructing the potential energy surface for reactions of a molecule with the surface of cleaved non-conducting crystals is reported. The method uses systematic fragmentation to express the total potential in terms of potential energy surfaces which describe reactions of relatively small molecules in the gas phase. The approach is illustrated by an application to the reaction of hydrogen atoms with a hydrogen-terminated silicon(111) surface.     

Potential energy surfaces for OsH2

Summary We compute the potential energy surfaces of 12 electronic states of OsH₂ (four quintet, four triplet, and four singlet) arising from⁵ D ground state of the Os atom as well as triplet and singlet excited states using the complete active space multiconfiguration self-consistent field (CAS-MCSCF) followed by multireference configuration interaction (MRCI) and relativistic CI (RCI) calculation which include up to 430,000 configurations. We find that the⁵ D ground state of Os atom does not insert into H₂ while the excited³ F state of Os does. The³ B ₁ ground state of OsH₂ (there are two other nearly degenerate states) in the absence of spin-orbit coupling was found to be 22 kcal/mol more stable than Os(⁵ D)+H₂. The spin-orbit mixing of³ B ₁,³ B ₂,³ A ₂, and¹ A ₁ states was so strong that it induces significant change in bond angles (up to 10°) for OsH₂.Dedicated to Prof. Klaus RuedenbergCamille and Henry Dreyfus Teacher-Scholar     

Potential energy surfaces for rearrangements of Berson trimethylenemethanes

In this research, thermal rearrangements of the Berson trimethylenemethanes (Berson-TMMs) have been investigated by employing density functional theory (DFT) and high-level ab initio methods, such as the complete active space self-consistent field (CASSCF), multireference second-order M?ller-Plesset perturbation theory (MRMP2), multireference configuration interaction singles and doubles (MRCISD), and coupled-cluster singles and doubles with perturbative triples [CCSD(T)]. In all computations Pople's polarized triple-ζ split valence basis set, 6-311G(d,p), is utilized. The relevant portions of the lowest-energy, singlet-spin potential energy surface of the C(4)H(6) (parent TMM), C(6)H(8) (Berson-TMMa), and C(8)H(12) (Berson-TMMc) chemical systems have been explored in order to determine the reaction energies and activation parameters accurately, with the ultimate objective of providing a theoretical account of experiments by Berson on TMMc. The nature of the orthogonal and the planar structures of the parent TMM have been clarified in this study. We have concluded that the orthogonal TMM (1)B(1) minimum has a C(2v) symmetry structure, and there is no pyramidalization in the unique methylene group. It lies at 13.9 kcal mol(-1) above the triplet minimum (3)B(2) at MRCISD level. The closed-shell (1)A(1) state of the planar TMM is not a true minimum but a transition structure (TS) for 180° rotation of the unique methylene group in the orthogonal TMM minimum. It lies at 3.0 kcal mol(-1) above (1)B(1). The planar structures are also involved in the interchange of equivalent orthogonal TMMs (o(1), o(2), o(3)). Many features of the parent TMM are retained in TMMa and TMMc, despite the constraints imposed by the five-membered ring in the latter species. Thus, ring closure to the bicyclic molecules 3a (3c) and 5a (5c) takes place similarly to that in the parent TMM. Likewise, planar TMMa (TMMc) structures are TSs, while orthogonal ones are true minima. The adiabatic singlet-triplet gaps are also similar, being 14.7 (13.0) and 16.5 (16.2) kcal mol(-1) in the orthogonal (o(1)) and planar TMMa (TMMc), respectively. It has been shown here that the substantial reductions in the ring-opening barriers of MCP derivatives 3a (3c) and 5a (5c) can be largely attributed to ring strain in the former and π-bond strain in the latter species.     

Exploring the free energy surfaces of clusters using reconnaissance metadynamics

A new approach is proposed for exploring the low-energy structures of small to medium-sized aggregates of atoms and molecules. This approach uses the recently proposed reconnaissance metadynamics method [G. A. Tribello, M. Ceriotti, and M. Parrinello. Proc. Natl. Acad. Sci. U.S.A. 107(41), 17509 (2010)] in tandem with collective variables that describe the average structure of the coordination sphere around the atoms/molecules. We demonstrate this method on both Lennard-Jones and water clusters and show how it is able to quickly find the global minimum in the potential energy surface, while exploring the finite temperature free energy surface.     

Kinetic energy release during evaporation from large sodium clusters

We have measured the distribution of momenta of atoms evaporating from large sodium clusters produced in a supersonic expansion source. The distributions are well described by phase space theory when polarization effects are included in the atomic capture cross section. Alternatively, the data can be fitted by a simple powerlaw preexponential. The cluster temperature extracted from both models differ, but still agree reasonable well with evaporative ensemble predictions. The data rule out a non-trivial transition state.     

Potential energy surfaces of SimOn cluster formation and isomerization

The reaction paths for formation and isomerization of a set of silica SimOn (m = 2,3, n = 1-5) nanoclusters have been investigated using second-order perturbation theory (MP2) with the 6-31G(d) basis set. The MP2/6-31G(d) calculations have predicted singlet ground states for all clusters excluding Si3O2. The total energies of the most important points on the potential energy surfaces (PES) have been determined using the completely renormalized (CR) singles and doubles coupled cluster method including perturbative triples, CR-CCSD(T) with the cc-pVTZ basis set. Although transition states have been located for many isomerization reactions, only for Si3O3 and Si3O4 have some transition states been found for the formation of a cluster from the separated reactants. In all other cases, the process of formation of SimOn clusters appears to proceed without potential energy barriers.     

Potential energy surfaces for BeH2 and BH2

The diatomics-in-molecules method has been used to obtain potential energy surfaces (PES) for the molecules BeH₂ and BH₂. The method is used in a way proposed by Tully [1]. The present paper contains an analysis of some features of PES in the vicinity of their crossing near linear configurations of the molecules.     

Potential energy surfaces for low-lying electronic states of SO_2

The sulfur dioxide molecule (SO2) is an important atmospheric pollutant primarily from sulfur-containing materials combustion processes[1]. Because of its im- portance in atmospheric photochemistry, as well as in atmospheric dynamics, this molecule has been the subject of much experimental[2―10] and theoreti- cal[11―19] photochemical study for many years. They provide a wealth of information about the SO2 spec- trum, predissociation mechanism, vibration including vibration-rotation interact…     

Metal clusters and surfaces

The point of view of a physical chemist interested in metal clusters because of their connection with heterogeneous catalysis is illustrated. The analogies and differences between clusters and surfaces are given special attention. After a review of experimental techniques and of types of clusters studied, very important questions of theory are briefly considered, with special reference to Lauher's rules for predicting the stoichiometry of clusters. The relevance of clusters to surface studies is discussed also with reference to fluxionality and reactivity.     

Adlayer morphologies and free energy landscapes of clusters of bis-fullerenes on model gold surfaces

There have been a few experimental reports of self-assembled adlayers of bis-fullerene molecules on solid substrates. Most of these studies suggest the adsorbate molecules are lying down on the surface, with the fullerene moieties almost close packed. However, very little theoretical work has been carried out on such systems, and little is known about the roles played by different parts of the potential energy in driving the self-assembly. We carry out a Temperature Replica Exchange Monte Carlo study here of two representative bis-fullerene molecules on a metal substrate. We use a coarse-grained model potential energy function, in which certain parameters can be varied within the range of their experimental uncertainty. The molecules investigated consist of two fullerene moieties bonded by a rigid bridging group. In particular, the effect of the strength of the fullerene interaction E(FG) with the substrate (nominally Au(111)) has been investigated in detail. To ensure efficient sampling of the rugged potential energy surfaces encountered in the simulations, we utilize replica exchange techniques. These enable us to construct free energy landscapes for the system. We find that for relatively low values of E(FG) the molecules form standing-up adlayers. By contrast, for higher values of E(FG), lying-down adlayers dominate. For one molecule, two different crystalline adlayer morphologies have been identified. The detailed structure of the lying-down layer is a function of the temperature and of the group used to bridge the fullerene moieties.     

Potential energy surfaces and vibrational spectra for isotopomers of N2O

Potential energy surfaces and vibrational spectra for the four isotopomers (^l5N¹⁴N¹⁶O,^l4N^I5N¹⁶O,¹⁵N₂ ¹⁶O and¹⁵N₂ ¹⁸O) of N₂O have been investigated with the vibrational self-consistent field-configuration interaction method. It is shown that the isotopomers with the same end atom have similar values of the potential parameters, and that substitution with different end atoms can affect the potential obviously. The calculated vibrational levels are in good agreement with the observed values by the optimization of several potential parameters (f ₁ ⁽¹⁾,f ₁₃ ⁽⁰⁾,f ₃ ⁽¹⁾ which are sensitive to isotopic substitutions. Project supported by the National Natural Science Foundation of China (Grant No. 29673029).     

Potential energy surfaces and vibrational spectra for isotopomers of N_2O

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Potential energy surfaces and Jahn-Teller effect on CH4...NO complexes

The potential energy surface of the CH(4)...NO van der Waals complexes was explored at the RCCSD(T)/aug-cc-pVTZ level including the full counterpoise correction to the basis set superposition error. The Jahn-Teller distortion of the C(3v) configurations for the CH bonded and CH(3) face complexes was analyzed. From this distortion, two A(') and A(") adiabatic surfaces were considered. The estimated zero point energy of C(s) configurations is above the barrier of the C(3v) ones. Therefore, the CH(3) face complexes are dynamic Jahn-Teller systems. The D(0) (140 cm(-1) for A(") state and 100 cm(-1) for A(')) values obtained are in good agreement with the experimental values (103+/-2 cm(-1)) recently reported.     

Potential energy surfaces for a mixed-valence dimer in an applied electric field

Summary A mixed-valence dimer with an applied external field aligned along the internuclear axis is studied using a two-site small-polaron model. Potential energy surfaces are calculated in the adiabatic (Born-Oppenheimer) approximation. It is shown that two nuclear coordinates (one totally symmetric and the other antisymmetric) are coupled to the electronic motion, whereas only the antisymmetric coordinate is coupled in the absence of an electric field. For a strongly localized (valence trapped) system, the displacement along the totally symmetric coordinate is directly proportional to the applied field strength. For delocalized (valence-averaged) systems, there is significant displacement along the antisymmetric coordinate, an effect which also vanishes in the absence of an applied field. Contributions to the linewidth are estimated.On sabbatical leave at Aarhus University through March 1994.     

Potential energy surfaces for small alcohol dimers I: methanol and ethanol

Potential energy landscapes for homogeneous dimers of methanol and ethanol were calculated using counterpoise (CP) corrected energies at the MP26-311+G(2df,2pd) level. The landscapes were sampled at approximately 15 dimer separation distances for different relative monomer geometries, or routes, given in terms of a relative monomer yaw, pitch, and roll and the spherical angles between the monomer centers (taken as the C atom attached to the O). The 19 different routes studied for methanol and the 22 routes examined for ethanol include 607 CP corrected energies. Both landscapes can be adequately represented by site-site, pairwise-additive models, suitable for use in molecular simulations. A modified Morse potential is used for the individual pair interactions either with or without point charges to represent the monomer charge distribution. A slightly better representation of the methanol landscape is obtained using point charges, while the potential energy landscape of ethanol is slightly better without point charges. This latter representation may be computationally advantageous for molecular simulations because it avoids difficulties associated with long-range effects of point-charge-type models.