Nonempirical Atom‐Atom Potentials for Main Components of Intermolecular Interaction Energy

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The hybrid method having features of ab-initio crystal orbital and ab-initio molecular cluster methods is proposed. In the approach presented the molecular crystal is treated as an infinite chain in a direction z, while two other directions are simulated by finite interactions ofthe molecular type. The new approach is especially useful for an investigation of anisotropic crystals. Test calculations for the carbon dioxide crystal are presented. The method was also employed for the investigation of a dissociation pathway of C-N bond in nitromethane in nitromethane crystal.

Section: Outline Of the Methodsmentioning

confidence: 99%

TheAb-Initio hybrid crystal orbital/molecular cluster approach to study the electronic structure of molecular crystals and reactions in the solid environment

Roszak

Kaufman

1991

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“…Our treatment of this contribution includes explicitly its anisotropy. We have recently shown [20,21] that the electrostatic term is the dominant contribution to anisotropy. Since we calculate this term explicitly, we take into account the anisotropy of intermolecular interactions.…”

Section: B Ab Lnitio Scf Interaction Energy Decomposition Scheme Comentioning

confidence: 99%

“…M B p intermolecular interaction energy includes both intermolecular correlation energy and the correlation contribution to the intermolecular interaction energy from correlated intramolecular (monomer) wave functions. For precise notation we shall denote our calculated electrostatic interaction energy EgL);: by Ei2sE$MBTP (4) . W e calculated E,,Mp"'Sw MBTP(4) for the nitromethane dimer using the correlated multipoles from nitromethane second-order dispersion energy calculated within variation-perturbation procedure [8].…”

Section: B Intermolecular Interaction Energy Component From Use Of mentioning

confidence: 99%

“…We have a long-standing interest in ab initio calculations of potential energy surfaces of nitrocompounds for their intramolecular decomposition: GVB [ 11, CASSCF [2] (complete active space MC-SCF) and MRD-CI [ 1-31 (multireference double excitationconfiguration interaction) [using both all-electron atomic basis sets of various sizes and our ab initio valence-electron MODPOT (ab initio effective core model potential) basis set]; SCF intermolecular interaction calculations [4] (using our ab initio MODPOT basis set) and energy-partitioned ab initio intermolecular calculations plus a semitheoretical estimate for the dispersion energy [4].…”

Section: Introductionmentioning

confidence: 99%

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Comparison of ab initioMODPOT interaction energy components against large basis set MBPT (4) calculations for nitromethane dimer

Sokalski

Hariharan

Kaufman

1987

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Ab-Initio MODPOT SCE calculations using our own optimized well-balanced minimal basis sets have little basis set superposition error (BSSE) and have proven over the years to give reliable intermolecular geometries and interaction energies. Another approach, using ab initio potential functions from energy partitioned ab initio calculations, has also yielded reliable interaction energies and intermolecular geometries, including crystal structures.We used both of these techniques in comparing the results of a published large all-electron basis set calculation on the nitromethane dimer with the above methods. Our SCF intermolecular minimum energy was at the same internuclear distance as the large all-electron basis set. Our SCF interaction energy, corrected for BSSE, was only 0.4 kcal above the SCF energy of the large basis set sCF calculation corrected for BSSE. We also calculated the energy partitioned components with our ab initio MODPOT basis set and with the larger all-electron basis set and showed that the small difference in interaction energy was due to a small difference in the first-order electrostatic multipolar term. (We also calculated this term from correlated wave functions [SDQ-MBFT (4)] using both ab initio MODPOT and the larger all-electron basis sets). From values of the fist-order electrostatic multipolar term from SCF and correlated monomer wave functions, the contribution to intermolecular interaction energy due to the use of correlated monomer wave functions has been estimated. Our results indicate either the dominant role of electrostatic term or near cancellation of the remaining components of intermolecular interaction energy. For cyclic nitromethane dimer at equilibrium distance these effects approach 0.9 kcal/mol (nearly ?4 of total interaction energy). In addition, we showed that the semitheoretical expression and parameters we use for estimating the dispersion energy gave results very close to the published variationperturbation results from the larger basis set calculation.

“…ab initio atomic multipoles presented in this contribution constitute an indispensable supplement to nonempirical atom-atom potentials [ 25 ] enabling the calculation of the intermolecular interaction energy and its components, as well as in studying other properties of proteins derivable from multipole expansion.…”

mentioning

confidence: 99%

Library of cumulative atomic multipole moments: II. neutral and charged amino acids

Sokalski¹,

Maruszewski²,

Hariharan

et al. 2009

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Cumulative atomic multipole moments (CAMM) for 28 neutral and charged forms of naturally occurring amino acids have been obtained from ab initio LCAO-MO-SCF wave functions using the all valence MODPOT basis set with nonempincal effective core model potentials. CAMMS provide a compact and condensed representation of the molecular charge distribution at atomic resolution. They may be used to obtain satisfactory nonempirical estimates of anisotropic properties of various biomolecules that are responsible for their specific interactions, i.e., molecular electrostatic potentials, electric fields, field gradients, etc., as well as intermolecular interaction energies between polar and/or charged constituents. To facilitate calculations for large proteins, we present in this paper CAMMs for all neutral and charged forms of amino acids to supplement our previously published data for nucleic acid bases.' The utility of this part of our data base has been demonstrated by calculation of histidine (HIS64) pK shifts resulting from single amino acid substitutions in several subtilisine [ E.C.3.4.4.161 mutant enzymes engineered by sitedirected mutagenesis technique.