The Experts below are selected from a list of 50865 Experts worldwide ranked by ideXlab platform
Jiři Pittner - One of the best experts on this subject based on the ideXlab platform.
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uncoupled multireference state specific mukherjee s coupled cluster method with triexcitations
Journal of Chemical Physics, 2010Co-Authors: Ondřej Demel, Kiran Bhaskarannair, Jiři PittnerAbstract:We have developed the uncoupled version of multireference Mukherjee’s coupled cluster method with connected triexcitations. The method has been implemented in ACES II program package. The agreement between the uncoupled and the standard version of Mukherjee’s multireference coupled cluster method has been reported previously at the singles and doubles level by Das et al. [J. Mol. Struct.: THEOCHEM 79, 771 (2006); Chem. Phys. 349, 115 (2008)]. The aim of this article is to investigate this method further, in order to establish how its performance changes with the size of the basis set, size of the model space, multireference character of different Molecules, and inclusion of connected triple excitations. Assessment of the new method has been performed on the singlet methylene, potential energy curve of fluorine Molecule, and third b Σ1g+ electronic state of Oxygen Molecule.
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multireference mukherjee s coupled cluster method with triexcitations in the linked formulation efficient implementation and applications
Journal of Chemical Physics, 2010Co-Authors: Kiran Bhaskarannair, Ondřej Demel, Jiři PittnerAbstract:We have formulated the multireference Mukherjee’s coupled clusters method with triexcitations (MR MkCCSDT) in the linked version and implemented it in the ACES II program package. The assessment of the new method has been performed on the first three electronic states of the Oxygen Molecule, on studies of singlet-triplet gap in methylene and twisted ethylene, where a comparison with other multireference CC treatments and with experimental data is available. The MR MkCCSDT results show accuracy comparable to which can be achieved with CCSDT in single reference cases. Comparison of the previously developed MkCCSD(T) method with MkCCSDT as a reference suggests, that MkCCSD(T) might be a promising candidate for an accurate treatment of systems where the static correlation plays an important role, at least for situations where small model spaces are sufficient.
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multireference brillouin wigner coupled clusters method with noniterative perturbative connected triples
Journal of Chemical Physics, 2006Co-Authors: Ondřej Demel, Jiři PittnerAbstract:We developed and implemented the state-specific Brillouin-Wigner coupled cluster method with singles, doubles, and noniterative perturbative triples, called MR BWCCSD(T), for a general number of closed- and open-shell reference configurations. To assess the accuracy of the method, we performed calculations of the three lowest electronic states of the Oxygen Molecule and of the automerization barrier of cyclobutadiene. For the Oxygen Molecule, the results were in a good agreement in comparison with those of the iterative MR BWCCSDTα method. For cyclobutadiene, the effect of connected triples was found to be minor, which is in agreement with the previous study by and Balkova and Bartlett [J. Chem. Phys. 101, 8972 (1994)].
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towards the multireference brillouin wigner coupled clusters method with iterative connected triples mr bwccsdt α approximation
Journal of Chemical Physics, 2005Co-Authors: Jiři Pittner, Ondřej DemelAbstract:We developed and implemented an approximation of the state-specific Brillouin–Wigner coupled-cluster method with singles, doubles, and triples, called MRBWCCSDT-α, for a general number of closed- and open-shell reference configurations. The accuracy of the method is assessed on the calculation of the Oxygen Molecule in the X3Σg−, a1Δg, and b1Σg+ states and the results of this multireference treatment are compared with previous MRBWCCSD results and with those obtained by the doubly ionized similarity transformed equation-of-motion CCSD and multireference configuration interaction methods and with experimental spectroscopic data. Explicit tests of the size-extensivity of the MRBWCCSDT-α method with iterative size-extensivity correction are also performed.
Ondřej Demel - One of the best experts on this subject based on the ideXlab platform.
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uncoupled multireference state specific mukherjee s coupled cluster method with triexcitations
Journal of Chemical Physics, 2010Co-Authors: Ondřej Demel, Kiran Bhaskarannair, Jiři PittnerAbstract:We have developed the uncoupled version of multireference Mukherjee’s coupled cluster method with connected triexcitations. The method has been implemented in ACES II program package. The agreement between the uncoupled and the standard version of Mukherjee’s multireference coupled cluster method has been reported previously at the singles and doubles level by Das et al. [J. Mol. Struct.: THEOCHEM 79, 771 (2006); Chem. Phys. 349, 115 (2008)]. The aim of this article is to investigate this method further, in order to establish how its performance changes with the size of the basis set, size of the model space, multireference character of different Molecules, and inclusion of connected triple excitations. Assessment of the new method has been performed on the singlet methylene, potential energy curve of fluorine Molecule, and third b Σ1g+ electronic state of Oxygen Molecule.
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multireference mukherjee s coupled cluster method with triexcitations in the linked formulation efficient implementation and applications
Journal of Chemical Physics, 2010Co-Authors: Kiran Bhaskarannair, Ondřej Demel, Jiři PittnerAbstract:We have formulated the multireference Mukherjee’s coupled clusters method with triexcitations (MR MkCCSDT) in the linked version and implemented it in the ACES II program package. The assessment of the new method has been performed on the first three electronic states of the Oxygen Molecule, on studies of singlet-triplet gap in methylene and twisted ethylene, where a comparison with other multireference CC treatments and with experimental data is available. The MR MkCCSDT results show accuracy comparable to which can be achieved with CCSDT in single reference cases. Comparison of the previously developed MkCCSD(T) method with MkCCSDT as a reference suggests, that MkCCSD(T) might be a promising candidate for an accurate treatment of systems where the static correlation plays an important role, at least for situations where small model spaces are sufficient.
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multireference brillouin wigner coupled clusters method with noniterative perturbative connected triples
Journal of Chemical Physics, 2006Co-Authors: Ondřej Demel, Jiři PittnerAbstract:We developed and implemented the state-specific Brillouin-Wigner coupled cluster method with singles, doubles, and noniterative perturbative triples, called MR BWCCSD(T), for a general number of closed- and open-shell reference configurations. To assess the accuracy of the method, we performed calculations of the three lowest electronic states of the Oxygen Molecule and of the automerization barrier of cyclobutadiene. For the Oxygen Molecule, the results were in a good agreement in comparison with those of the iterative MR BWCCSDTα method. For cyclobutadiene, the effect of connected triples was found to be minor, which is in agreement with the previous study by and Balkova and Bartlett [J. Chem. Phys. 101, 8972 (1994)].
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towards the multireference brillouin wigner coupled clusters method with iterative connected triples mr bwccsdt α approximation
Journal of Chemical Physics, 2005Co-Authors: Jiři Pittner, Ondřej DemelAbstract:We developed and implemented an approximation of the state-specific Brillouin–Wigner coupled-cluster method with singles, doubles, and triples, called MRBWCCSDT-α, for a general number of closed- and open-shell reference configurations. The accuracy of the method is assessed on the calculation of the Oxygen Molecule in the X3Σg−, a1Δg, and b1Σg+ states and the results of this multireference treatment are compared with previous MRBWCCSD results and with those obtained by the doubly ionized similarity transformed equation-of-motion CCSD and multireference configuration interaction methods and with experimental spectroscopic data. Explicit tests of the size-extensivity of the MRBWCCSDT-α method with iterative size-extensivity correction are also performed.
Jirri Pittner - One of the best experts on this subject based on the ideXlab platform.
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Multireference state-specific Mukherjee's coupled cluster method with noniterative triexcitations.
The Journal of chemical physics, 2008Co-Authors: Kiran Bhaskaran-nair, Ondrej Demel, Jirri PittnerAbstract:We have formulated and implemented the multireference Mukherjee’s coupled cluster method with connected singles, doubles, and perturbative triples [MR MkCCSD(T)] in the ACES II program package. Assessment of the new method has been performed on the first three electronic states of the Oxygen Molecule and on the automerization barrier of cyclobutadiene, where a comparison with other multireference CC treatments and with experimental data where available. The MR MkCCSD(T) method seems to be a promising candidate for an accurate, yet computationally tractable, treatment of systems where the static correlation plays an important role.
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multireference brillouin wigner coupled cluster method with singles doubles and triples efficient implementation and comparison with approximate approaches
Journal of Chemical Physics, 2008Co-Authors: Ondrej Demel, Jirri PittnerAbstract:We have developed an efficient implementation of the multireference Brillouin–Wigner coupled cluster method with full iterative treatment of connected singles, doubles, and triples. Its computational costs are too high for applications to larger Molecules; however, it can be used as a useful tool for benchmarking approximate methods. Performance of the method has been tested on the ground and low-lying excited states of the Oxygen Molecule and on the singlet-triplet gap in methylene; the results are in good agreement with experimental data.
Ondrej Demel - One of the best experts on this subject based on the ideXlab platform.
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Multireference state-specific Mukherjee's coupled cluster method with noniterative triexcitations.
The Journal of chemical physics, 2008Co-Authors: Kiran Bhaskaran-nair, Ondrej Demel, Jirri PittnerAbstract:We have formulated and implemented the multireference Mukherjee’s coupled cluster method with connected singles, doubles, and perturbative triples [MR MkCCSD(T)] in the ACES II program package. Assessment of the new method has been performed on the first three electronic states of the Oxygen Molecule and on the automerization barrier of cyclobutadiene, where a comparison with other multireference CC treatments and with experimental data where available. The MR MkCCSD(T) method seems to be a promising candidate for an accurate, yet computationally tractable, treatment of systems where the static correlation plays an important role.
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multireference brillouin wigner coupled cluster method with singles doubles and triples efficient implementation and comparison with approximate approaches
Journal of Chemical Physics, 2008Co-Authors: Ondrej Demel, Jirri PittnerAbstract:We have developed an efficient implementation of the multireference Brillouin–Wigner coupled cluster method with full iterative treatment of connected singles, doubles, and triples. Its computational costs are too high for applications to larger Molecules; however, it can be used as a useful tool for benchmarking approximate methods. Performance of the method has been tested on the ground and low-lying excited states of the Oxygen Molecule and on the singlet-triplet gap in methylene; the results are in good agreement with experimental data.
E I Yuryeva - One of the best experts on this subject based on the ideXlab platform.
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chemical bonding and quadrupole splittings of 57fe mossbauer spectrum in active sites of oxyhemoglobin as calculated by xα discrete variation method
Hyperfine Interactions, 2008Co-Authors: E I YuryevaAbstract:Results of quantum-chemical X α -discrete variation method (X α -DVM) calculations of interaction parameters between iron (II) and Oxygen Molecule in active sites of α- and β-subunits of oxyhemoglobin are presented within three models: without extra electron and in spin-unrestricted mode (model I); without extra electron and in spin-restricted mode (model II); with extra electrons in spin-unrestricted mode (model III). The electronic structure and 57Fe quadrupole splitting ΔE Q for the active site of α- and β-subunits (within model I) and only of the α-subunit (within models II and III) of oxyhemoglobin are calculated. The differences in ΔE Q values for these three models are discussed.
