ABSTRACT Recently we have written a new program POLY-CRYST to calculate ab-initio orbitals for mo... more ABSTRACT Recently we have written a new program POLY-CRYST to calculate ab-initio orbitals for molecular crystals and polymers. This technique makes use of the translational symmetry in a crystal and the translational and/or translational rotational symmetry in a polymer. Into this new POLY-CRYST program we meshed, as options, all of our desirable optimal computational strategies for ab-initio calculations on large molecules. The results of preliminary test calculations are presented.
Abstract Recently we derived, implemented, tested and used successfully a new computational strat... more Abstract Recently we derived, implemented, tested and used successfully a new computational strategy for ab-initio MRD-CI (multireference double excitation-configuration interaction) calculations for molecular decompositions of large molecules and intermolecular reactions of large systems. We carry out the ab-initio SCF for the entire system, then transform the canonical delocalized molecular orbitals to localized orbitals and include explicitly in the MRD-CI only the localized occupied and virtual orbitals in the region of interest, folding the remainder of the occupied localized orbitals into an “effective” CI Hamiltonian. The advantage is that the transformations from integrals over atomic orbitals to integrals over molecular orbitals (the computer time-, computer core- and external storage-consuming part of the CI calculations) only have to be carried out for the localized orbitals included explicitly in the MRD-CI calculations. The challenge arose to extend our MRD-CI technique based on localized/local orbitals and “effective” CI Hamiltonian to the breaking of a chemical bond in a molecule in a crystal (or other solid environment). This past year we have derived, implemented and used successfully a procedure for doing this. Our technique involves solving a quantum chemical ab-initio SCF explicitly for a system of a reference molecule surrounded by a number of other molecules in the multipole environment of yet more further out surrounding molecules. The resulting canonical molecular orbitals are then localized and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-I calculations are then carried out for breaking a bond in the reference molecule. This method is completely general. The space treated explicitly quantum chemically and the surrounding space can have defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. We have applied this procedure successfully to the H3CNO2 bond dissociation of nitromethane with extensive testing of the number of molecules that have to be included explicitly in the SCF and how many further out molecules have to be represented by multipoles. To check the goodness of the model cluster approximation for crystalline nitromethane, we carried out ab-initio crystal orbital (XTLORB) calculations using our POLY-CRYST program. The difference in the XTLORB total energies between the 4 nitromethane molecules/unit cell and the 3 nitromethane molecules/unit cell, ER = E4 − E3 = − 48.0609079 a.u., corresponds very closely to the reduced energy per nitromethane molecule, ER = − 48.06057 a.u., calculated from explicit SCF calculations on the model nitromethane cluster in the multipole field of farther out nitromethane molecules for the model cluster. Thus, the multipole approximation for describing the effect of further out molecules on the SCF cluster energies is quite good.
The difference electrostatic molecular potential contour maps [11 (EMP) provide some useful infor... more The difference electrostatic molecular potential contour maps [11 (EMP) provide some useful information concerning the effect of aggregation of chemical compounds on their interactions, in particular on their electrostatic component. Existing experimental evidence ...
This report contains copies of nearly all of the technical papers and viewgraphs presented at the... more This report contains copies of nearly all of the technical papers and viewgraphs presented at the NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Application. This conference served as a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include the following: magnetic disk and tape technologies; optical disk and tape; software storage and file management systems; and experiences with the use of a large, distributed storage system. The technical presentations describe, among other things, integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's. Separate abstracts were prepared for papers in this report.
Proceedings of IEEE 14th Symposium on Mass Storage Systems
Mission to Planet Earth (MTPE) is a long-term NASA re-search mission to study the processes leadi... more Mission to Planet Earth (MTPE) is a long-term NASA re-search mission to study the processes leading to global climate change. The EOS Data and Information System (EOSDIS) is the component within MTPE that will pro-vide the Earth science community with easy, affordable, and ...
... with real molecular orbitals is used, leading to the well-known equations of Roothaan [13] fo... more ... with real molecular orbitals is used, leading to the well-known equations of Roothaan [13] for the expansion coefficients. For states of higher multiplicity, unrestricted single-determinant theory is used (different orbitals for different spins) leading to generalized equations [14]. ...
Atom-atom potentials representing separate contributions to the nonempirical interaction energy h... more Atom-atom potentials representing separate contributions to the nonempirical interaction energy have been derived in the SCF decomposition scheme corrected for basis set superposition error by the counter-poise method. The nontransferable long-range electrostatic multipole and ...
In the propagation step of the cationic polymerization, oxetane reacts with the protonated oxetan... more In the propagation step of the cationic polymerization, oxetane reacts with the protonated oxetane formed in the initiation step, with concomitant ring opening of the protonated oxetane. To describe properly bond making or bond breaking, it is necessary to use MC-SCF or CI calculations. We have carried out ab initio MODPOT/VRDDO MRD-CI calculations (by the multireference double excitation–configuration interaction technique of Buenker and Peyerimhoff into which we have also meshed a number of desirable computational options for ab initio calculations on large molecules). The CI calculations were carried out on strictly orthogonalized localized occupied and virtual orbitals in the reaction region, with the remainder of the occupied molecular orbitals being folded into an effective CI Hamiltonian. The calculated potential energy surfaces indicate that a preferred pathway for this reaction resembles an SN2 reaction with the oxygen of the oxetane attacking linearly along the C4O direction of the protonated oxetane and inversion of the hydrogens around the C4 atom.
Recently we extended our strategy for MRD-CI (multireference double excitation-configuration inte... more Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an "effective" CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment. Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an "effective" CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. Dimethylnitramine is the smallest prototype of the energetic R2N-N02 nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is
The structures of the cations CH + 3 , CH + 5 , C 2 H + 3 and C 2 H + 5 are examined by ab initio... more The structures of the cations CH + 3 , CH + 5 , C 2 H + 3 and C 2 H + 5 are examined by ab initio molecular orbital theory. A systematic procedure for improving the basis set and refining the equilibrium geometry is used. It is found that the addition of polarization functions (d-functions on ...
Topics in Current Chemistry Fortschritte der Chemischen Forschung
We investigated the structures and the stabilities of the three-membered rings F n X-CH 2-Y (X) S... more We investigated the structures and the stabilities of the three-membered rings F n X-CH 2-Y (X) Si, P, S; Y) CH 2 , NH, O; n) 2 or 3) containing a hypervalent atom (X) and disclosed their origins by developing and applying an electron-pair bond model for hypervalent molecules. For the rings containing a pentacoordinated Si or P atom, the (ap, eq) isomers with the ring bonds in the apical and equatorial positions are local minima, while the (eq, eq) isomers with both ring bonds in the equatorial positions are the transition states of pseudorotation reactions due to the high ring strains. In contrast, the (ap, eq) and (eq, eq) isomers for the rings containing a tetracoordinated P or S atom are both local minima. The tetracoordinated species are less strained than the pentacoordinated ones because of the effect of the lone pair on X giving rise to less antibonding properties of the electron delocalization between the geminal ring bonds on X. Moreover, the more strained (eq, eq) isomers are surprisingly more stable than the (ap, eq) isomers in most of the tetracoordinated species. The relative stabilities are controlled by the repulsion between the lone pair on X and the apical bond. The relative stabilities of the (ap, eq) isomers with Y () NH, O) in the apical and equatorial positions are predicted and discussed.
Journal of Physics B: Atomic and Molecular Physics, 1968
For the 2pδ state of the H2+ molecule the function ψ=(1+pRξ) exp(-αRξ) sinh(βRη) which is separab... more For the 2pδ state of the H2+ molecule the function ψ=(1+pRξ) exp(-αRξ) sinh(βRη) which is separable in elliptic coordinates, has been studied. The calculated energy is lower than that of any of the existing variational functions for 2 > 2. The integrals X2 and Z2 as well as the energy values for different nuclear separations have also been calculated.
Copies of nearly all of the technical papers and viewgraphs presented at the Goddard Conference o... more Copies of nearly all of the technical papers and viewgraphs presented at the Goddard Conference on Mass Storage Systems and Technologies held in Sep. 1992 are included. The conference served as an informational exchange forum for topics primarily relating to the ingestion and management of massive amounts of data and the attendant problems (data ingestion rates now approach the order of terabytes per day). Discussion topics include the IEEE Mass Storage System Reference Model, data archiving standards, high-performance storage devices, magnetic and magneto-optic storage systems, magnetic and optical recording technologies, high-performance helical scan recording systems, and low end helical scan tape drives. Additional topics addressed the evolution of the identifiable unit for processing purposes as data ingestion rates increase dramatically, and the present state of the art in mass storage technology.
The potential energy Curve of the system Lf/Eie has been determined with moderately large basis s... more The potential energy Curve of the system Lf/Eie has been determined with moderately large basis sets for 0.5 Q r 4 10.0 (10 both at the SCF level and including correIation. The present SCF results predict a deeper well (-0.00248 au) at a smaller r (3.66 an) compared with earlier calculations. Correlation deepens the weil further (-0.00274 au), but pulls it inward slighUy (3.63 uo). In the repulsive part the calculated curve lies above the experimental one, especially at shorter distances_ A similar behavior has been noted in the systems Li+/Hz, Li%ZO and Li+/Nz. suggesting that the experimental determinations may underestimate the interaction in this region by l&20%.
This document contains copies of those technical p apers received in time for publication prior t... more This document contains copies of those technical p apers received in time for publication prior to th e Fifth Goddard Conference on Mass Storage Systems and Technologies. As one of an ongoing series, th is conference continues to serve as a unique mediu m for the ...
ABSTRACT Recently we have written a new program POLY-CRYST to calculate ab-initio orbitals for mo... more ABSTRACT Recently we have written a new program POLY-CRYST to calculate ab-initio orbitals for molecular crystals and polymers. This technique makes use of the translational symmetry in a crystal and the translational and/or translational rotational symmetry in a polymer. Into this new POLY-CRYST program we meshed, as options, all of our desirable optimal computational strategies for ab-initio calculations on large molecules. The results of preliminary test calculations are presented.
Abstract Recently we derived, implemented, tested and used successfully a new computational strat... more Abstract Recently we derived, implemented, tested and used successfully a new computational strategy for ab-initio MRD-CI (multireference double excitation-configuration interaction) calculations for molecular decompositions of large molecules and intermolecular reactions of large systems. We carry out the ab-initio SCF for the entire system, then transform the canonical delocalized molecular orbitals to localized orbitals and include explicitly in the MRD-CI only the localized occupied and virtual orbitals in the region of interest, folding the remainder of the occupied localized orbitals into an “effective” CI Hamiltonian. The advantage is that the transformations from integrals over atomic orbitals to integrals over molecular orbitals (the computer time-, computer core- and external storage-consuming part of the CI calculations) only have to be carried out for the localized orbitals included explicitly in the MRD-CI calculations. The challenge arose to extend our MRD-CI technique based on localized/local orbitals and “effective” CI Hamiltonian to the breaking of a chemical bond in a molecule in a crystal (or other solid environment). This past year we have derived, implemented and used successfully a procedure for doing this. Our technique involves solving a quantum chemical ab-initio SCF explicitly for a system of a reference molecule surrounded by a number of other molecules in the multipole environment of yet more further out surrounding molecules. The resulting canonical molecular orbitals are then localized and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-I calculations are then carried out for breaking a bond in the reference molecule. This method is completely general. The space treated explicitly quantum chemically and the surrounding space can have defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. We have applied this procedure successfully to the H3CNO2 bond dissociation of nitromethane with extensive testing of the number of molecules that have to be included explicitly in the SCF and how many further out molecules have to be represented by multipoles. To check the goodness of the model cluster approximation for crystalline nitromethane, we carried out ab-initio crystal orbital (XTLORB) calculations using our POLY-CRYST program. The difference in the XTLORB total energies between the 4 nitromethane molecules/unit cell and the 3 nitromethane molecules/unit cell, ER = E4 − E3 = − 48.0609079 a.u., corresponds very closely to the reduced energy per nitromethane molecule, ER = − 48.06057 a.u., calculated from explicit SCF calculations on the model nitromethane cluster in the multipole field of farther out nitromethane molecules for the model cluster. Thus, the multipole approximation for describing the effect of further out molecules on the SCF cluster energies is quite good.
The difference electrostatic molecular potential contour maps [11 (EMP) provide some useful infor... more The difference electrostatic molecular potential contour maps [11 (EMP) provide some useful information concerning the effect of aggregation of chemical compounds on their interactions, in particular on their electrostatic component. Existing experimental evidence ...
This report contains copies of nearly all of the technical papers and viewgraphs presented at the... more This report contains copies of nearly all of the technical papers and viewgraphs presented at the NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Application. This conference served as a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include the following: magnetic disk and tape technologies; optical disk and tape; software storage and file management systems; and experiences with the use of a large, distributed storage system. The technical presentations describe, among other things, integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's. Separate abstracts were prepared for papers in this report.
Proceedings of IEEE 14th Symposium on Mass Storage Systems
Mission to Planet Earth (MTPE) is a long-term NASA re-search mission to study the processes leadi... more Mission to Planet Earth (MTPE) is a long-term NASA re-search mission to study the processes leading to global climate change. The EOS Data and Information System (EOSDIS) is the component within MTPE that will pro-vide the Earth science community with easy, affordable, and ...
... with real molecular orbitals is used, leading to the well-known equations of Roothaan [13] fo... more ... with real molecular orbitals is used, leading to the well-known equations of Roothaan [13] for the expansion coefficients. For states of higher multiplicity, unrestricted single-determinant theory is used (different orbitals for different spins) leading to generalized equations [14]. ...
Atom-atom potentials representing separate contributions to the nonempirical interaction energy h... more Atom-atom potentials representing separate contributions to the nonempirical interaction energy have been derived in the SCF decomposition scheme corrected for basis set superposition error by the counter-poise method. The nontransferable long-range electrostatic multipole and ...
In the propagation step of the cationic polymerization, oxetane reacts with the protonated oxetan... more In the propagation step of the cationic polymerization, oxetane reacts with the protonated oxetane formed in the initiation step, with concomitant ring opening of the protonated oxetane. To describe properly bond making or bond breaking, it is necessary to use MC-SCF or CI calculations. We have carried out ab initio MODPOT/VRDDO MRD-CI calculations (by the multireference double excitation–configuration interaction technique of Buenker and Peyerimhoff into which we have also meshed a number of desirable computational options for ab initio calculations on large molecules). The CI calculations were carried out on strictly orthogonalized localized occupied and virtual orbitals in the reaction region, with the remainder of the occupied molecular orbitals being folded into an effective CI Hamiltonian. The calculated potential energy surfaces indicate that a preferred pathway for this reaction resembles an SN2 reaction with the oxygen of the oxetane attacking linearly along the C4O direction of the protonated oxetane and inversion of the hydrogens around the C4 atom.
Recently we extended our strategy for MRD-CI (multireference double excitation-configuration inte... more Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an "effective" CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment. Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an "effective" CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. Dimethylnitramine is the smallest prototype of the energetic R2N-N02 nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is
The structures of the cations CH + 3 , CH + 5 , C 2 H + 3 and C 2 H + 5 are examined by ab initio... more The structures of the cations CH + 3 , CH + 5 , C 2 H + 3 and C 2 H + 5 are examined by ab initio molecular orbital theory. A systematic procedure for improving the basis set and refining the equilibrium geometry is used. It is found that the addition of polarization functions (d-functions on ...
Topics in Current Chemistry Fortschritte der Chemischen Forschung
We investigated the structures and the stabilities of the three-membered rings F n X-CH 2-Y (X) S... more We investigated the structures and the stabilities of the three-membered rings F n X-CH 2-Y (X) Si, P, S; Y) CH 2 , NH, O; n) 2 or 3) containing a hypervalent atom (X) and disclosed their origins by developing and applying an electron-pair bond model for hypervalent molecules. For the rings containing a pentacoordinated Si or P atom, the (ap, eq) isomers with the ring bonds in the apical and equatorial positions are local minima, while the (eq, eq) isomers with both ring bonds in the equatorial positions are the transition states of pseudorotation reactions due to the high ring strains. In contrast, the (ap, eq) and (eq, eq) isomers for the rings containing a tetracoordinated P or S atom are both local minima. The tetracoordinated species are less strained than the pentacoordinated ones because of the effect of the lone pair on X giving rise to less antibonding properties of the electron delocalization between the geminal ring bonds on X. Moreover, the more strained (eq, eq) isomers are surprisingly more stable than the (ap, eq) isomers in most of the tetracoordinated species. The relative stabilities are controlled by the repulsion between the lone pair on X and the apical bond. The relative stabilities of the (ap, eq) isomers with Y () NH, O) in the apical and equatorial positions are predicted and discussed.
Journal of Physics B: Atomic and Molecular Physics, 1968
For the 2pδ state of the H2+ molecule the function ψ=(1+pRξ) exp(-αRξ) sinh(βRη) which is separab... more For the 2pδ state of the H2+ molecule the function ψ=(1+pRξ) exp(-αRξ) sinh(βRη) which is separable in elliptic coordinates, has been studied. The calculated energy is lower than that of any of the existing variational functions for 2 > 2. The integrals X2 and Z2 as well as the energy values for different nuclear separations have also been calculated.
Copies of nearly all of the technical papers and viewgraphs presented at the Goddard Conference o... more Copies of nearly all of the technical papers and viewgraphs presented at the Goddard Conference on Mass Storage Systems and Technologies held in Sep. 1992 are included. The conference served as an informational exchange forum for topics primarily relating to the ingestion and management of massive amounts of data and the attendant problems (data ingestion rates now approach the order of terabytes per day). Discussion topics include the IEEE Mass Storage System Reference Model, data archiving standards, high-performance storage devices, magnetic and magneto-optic storage systems, magnetic and optical recording technologies, high-performance helical scan recording systems, and low end helical scan tape drives. Additional topics addressed the evolution of the identifiable unit for processing purposes as data ingestion rates increase dramatically, and the present state of the art in mass storage technology.
The potential energy Curve of the system Lf/Eie has been determined with moderately large basis s... more The potential energy Curve of the system Lf/Eie has been determined with moderately large basis sets for 0.5 Q r 4 10.0 (10 both at the SCF level and including correIation. The present SCF results predict a deeper well (-0.00248 au) at a smaller r (3.66 an) compared with earlier calculations. Correlation deepens the weil further (-0.00274 au), but pulls it inward slighUy (3.63 uo). In the repulsive part the calculated curve lies above the experimental one, especially at shorter distances_ A similar behavior has been noted in the systems Li+/Hz, Li%ZO and Li+/Nz. suggesting that the experimental determinations may underestimate the interaction in this region by l&20%.
This document contains copies of those technical p apers received in time for publication prior t... more This document contains copies of those technical p apers received in time for publication prior to th e Fifth Goddard Conference on Mass Storage Systems and Technologies. As one of an ongoing series, th is conference continues to serve as a unique mediu m for the ...
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Papers by P C Hariharan