The Experts below are selected from a list of 13962 Experts worldwide ranked by ideXlab platform
Wibe A De Jong - One of the best experts on this subject based on the ideXlab platform.
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pushing configuration interaction to the limit towards massively parallel mcscf Calculations
2017Co-Authors: Konstantinos D Vogiatzis, Jeppe Olsen, Laura Gagliardi, Wibe A De JongAbstract:A new large-scale parallel multiconfigurational self-consistent field (MCSCF) implementation in the open-source NWChem computational chemistry code is presented. The generalized active space approach is used to partition large configuration interaction (CI) vectors and generate a suffiCIent number of batches that can be distributed to the available cores. Massively parallel CI Calculations with large active spaces can be performed. The new parallel MCSCF implementation is tested for the chromium trimer and for an active space of 20 electrons in 20 orbitals, which can now routinely be performed. Unprecedented CI Calculations with an active space of 22 electrons in 22 orbitals for the pentacene systems were performed and a single CI iteration Calculation with an active space of 24 electrons in 24 orbitals for the chromium tetramer was possible. The chromium tetramer corresponds to a CI expansion of one trillion Slater determinants (914 058 513 424) and is the largest conventional CI Calculation attempted up to date.
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pushing configuration interaction to the limit towards massively parallel mcscf Calculations
2017Co-Authors: Konstantinos D Vogiatzis, Jeppe Olsen, Laura Gagliardi, Wibe A De JongAbstract:A new large-scale parallel multiconfigurational self-consistent field (MCSCF) implementation in the open-source NWChem computational chemistry code is presented. The generalized active space (GAS) approach is used to partition large configuration interaction (CI) vectors and generate a suffiCIent number of batches that can be distributed to the available nodes. Massively parallel CI Calculations with large active spaces can be treated. The performance of the new parallel MCSCF implementation is presented for the chromium trimer and for an active space of 20 electrons in 20 orbitals. Unprecedented CI Calculations with an active space of 22 electrons in 22 orbitals for the pentacene systems were performed and a single CI iteration Calculation with an active space of 24 electrons in 24 orbitals for the chromium tetramer was possible. The chromium tetramer corresponds to a CI expansion of one trillion SDs (914 058 513 424) and is largest conventional CI Calculation attempted up to date.
J Fiser - One of the best experts on this subject based on the ideXlab platform.
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multireference CI Calculation of nuclear quadrupole coupling constants of cn and cn rovibrational dependence
2002Co-Authors: R Polak, J FiserAbstract:Abstract The 14 N quadrupole coupling constants of rovibrational levels of the X 1 Σ + and c 1 Σ + states of CN + , and the ground electronic state of CN − are calculated from molecular wavefunctions which expliCItly describe nuclear displacement. From the electronic states considered, the exCIted 1 Σ + state of CN + is predicted to exhibit the strongest N coupling, at least in the ground vibrational state. Compared to the vibrational dependence of the 14 N QCC's, which is found to be significant in all cases, the rotational dependence is predicted to be unimportant. SpeCIal attention is paid to the assessment of adequacy of the expectation value approach to the evaluation of the electric field gradient tensor within the applied multireference configuration interaction formalism. Spectroscopic constants are derived from corresponding potential energy curves to testify to the quality of the correlated wave functions used.
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ab initio CI Calculation of nuclear quadrupole coupling constants of low lying rovibrational levels in the x 1σ state of ch
1993Co-Authors: J Fiser, J VoitikAbstract:Abstract The 2H and 11C quadrupole coupling constants of rovibrational levels of 12C2H+, and 11C2H+ in their ground electronic state have been calculated from molecular wavefunctions which expliCItly describe nuclear displacement. The deuteron coupling is found to be weak, its strength decreases with vibrational exCItation. The 11C coupling is predicted to be relatively very strong for both the isotopic variants. The vibrational dependence of the C coupling is found to be rather insignificant. The quadrupole hyperfine patterns of 11C2H+ are predicted to be dominated by the relatively very strong C coupling and their basic features are found to be independent of the vibrational state considered. The rotational dependence of both the 2H and 11C coupling constants is seen to be quite unimportant. The main features of the deuteron quadrupole coupling CH+ are analogous to those of the isoelectronic BH.
Nobuhiro Kosugi - One of the best experts on this subject based on the ideXlab platform.
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polarized one electron potentials fitted by multicenter polarizabilities and hyperpolarizabilities ab initio scf CI Calculation of water
1993Co-Authors: Setsuko Nakagawa, Nobuhiro KosugiAbstract:Abstract The electrostatic potential is usually evaluated by putting a test charge at several points on an appropriate molecular surface. The polarization effect is an indispensable long-range interaction as well as the electrostatic interaction. To evaluate the polarization effect, it is necessary to relax the wavefunction under the perturbed Hamiltonian. In the present work the polarized molecular potentials based on the ab initio SCF-CI method have been fitted by multicenter polarizabilities and hyperpolarizabilities. The polarization energies and induced dipole moments calculated by using the fitted parameters have been significantly improved by including the first hyperpolarizabilities in the case of a water molecule.
Konstantinos D Vogiatzis - One of the best experts on this subject based on the ideXlab platform.
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pushing configuration interaction to the limit towards massively parallel mcscf Calculations
2017Co-Authors: Konstantinos D Vogiatzis, Jeppe Olsen, Laura Gagliardi, Wibe A De JongAbstract:A new large-scale parallel multiconfigurational self-consistent field (MCSCF) implementation in the open-source NWChem computational chemistry code is presented. The generalized active space approach is used to partition large configuration interaction (CI) vectors and generate a suffiCIent number of batches that can be distributed to the available cores. Massively parallel CI Calculations with large active spaces can be performed. The new parallel MCSCF implementation is tested for the chromium trimer and for an active space of 20 electrons in 20 orbitals, which can now routinely be performed. Unprecedented CI Calculations with an active space of 22 electrons in 22 orbitals for the pentacene systems were performed and a single CI iteration Calculation with an active space of 24 electrons in 24 orbitals for the chromium tetramer was possible. The chromium tetramer corresponds to a CI expansion of one trillion Slater determinants (914 058 513 424) and is the largest conventional CI Calculation attempted up to date.
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pushing configuration interaction to the limit towards massively parallel mcscf Calculations
2017Co-Authors: Konstantinos D Vogiatzis, Jeppe Olsen, Laura Gagliardi, Wibe A De JongAbstract:A new large-scale parallel multiconfigurational self-consistent field (MCSCF) implementation in the open-source NWChem computational chemistry code is presented. The generalized active space (GAS) approach is used to partition large configuration interaction (CI) vectors and generate a suffiCIent number of batches that can be distributed to the available nodes. Massively parallel CI Calculations with large active spaces can be treated. The performance of the new parallel MCSCF implementation is presented for the chromium trimer and for an active space of 20 electrons in 20 orbitals. Unprecedented CI Calculations with an active space of 22 electrons in 22 orbitals for the pentacene systems were performed and a single CI iteration Calculation with an active space of 24 electrons in 24 orbitals for the chromium tetramer was possible. The chromium tetramer corresponds to a CI expansion of one trillion SDs (914 058 513 424) and is largest conventional CI Calculation attempted up to date.
Setsuko Nakagawa - One of the best experts on this subject based on the ideXlab platform.
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polarized one electron potentials fitted by multicenter polarizabilities and hyperpolarizabilities ab initio scf CI Calculation of water
1993Co-Authors: Setsuko Nakagawa, Nobuhiro KosugiAbstract:Abstract The electrostatic potential is usually evaluated by putting a test charge at several points on an appropriate molecular surface. The polarization effect is an indispensable long-range interaction as well as the electrostatic interaction. To evaluate the polarization effect, it is necessary to relax the wavefunction under the perturbed Hamiltonian. In the present work the polarized molecular potentials based on the ab initio SCF-CI method have been fitted by multicenter polarizabilities and hyperpolarizabilities. The polarization energies and induced dipole moments calculated by using the fitted parameters have been significantly improved by including the first hyperpolarizabilities in the case of a water molecule.