The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Rodney J Bartlett - One of the best experts on this subject based on the ideXlab platform.
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intermediate hamiltonian Fock Space multireference coupled cluster method with full triples for calculation of excitation energies
Journal of Chemical Physics, 2008Co-Authors: Monika Musial, Rodney J BartlettAbstract:The intermediate Hamiltonian multireference coupled-cluster (CC) method with singles, doubles, and triples within the excited (1,1) sector of Fock Space (FS) is implemented and formulated to calculate excitation energies (EEs). Due to the intermediate Hamiltonian formulation, which provides a robust computational scheme for solving the FS-CC equations, coupled to an efficient factorization strategy, relatively large basis sets and model Spaces are employed permitting basis set converged comparisons of the calculated vertical EEs, which can be compared to the experimental data for the N2 and CO molecules. The issue of charge-transfer separability is also addressed.
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Fock Space multireference coupled cluster method with full inclusion of connected triples for excitation energies
Journal of Chemical Physics, 2004Co-Authors: Monika Musial, Rodney J BartlettAbstract:We report the initial Fock Space multireference coupled cluster method with the full inclusion of single, double, and triple excitations (FS-CCSDT) for the (1,1) sector. We present pilot applications for calculating excitation energies for the N2 molecule and the Ne atom. The performance of the current model, along with the FS-CCSD one, has been studied in comparison with the equation-of-motion coupled-cluster and the similarity transformed methods.
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Fock Space multi reference coupled cluster study of excitation energies and dipole oscillator strengths of ozone
Chemical Physics Letters, 1992Co-Authors: Maria Barysz, Magnus Rittby, Rodney J BartlettAbstract:Abstract The singlet and triplet excitation energies are investigated by the Fock Space multi-reference coupled-cluster method. A procedure for evaluating dipole transition moments and oscillator strengths is also presented and applied. Good agreement is achieved for excitation energies and transition moments where experimental data are known.
Sourav Pal - One of the best experts on this subject based on the ideXlab platform.
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effect of triples to dipole moments in Fock Space multireference coupled cluster method
Journal of Chemical Theory and Computation, 2011Co-Authors: Lalitha Ravichandran, Nayana Vaval, Sourav PalAbstract:In this paper, we present the new implementation of partial triples for the dipole moment of doublet radicals in Lagrangian formulation of Fock-Space multireference coupled cluster (Λ-FSMRCC) response method. We have implemented a specific scheme of noniterative triples, in addition to singles and doubles schemes, which accounts for the effects appearing at least at the third order in dipole moments. The method is applied to the ground states of OH, OOH, HCOO, CN, CH, and PO radicals.
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on some aspects of Fock Space multi reference coupled cluster singles and doubles energies and optical properties
2010Co-Authors: Prashant Uday Manohar, Nayana Vaval, Kodagenahalli R Shamasundar, Arijit Bag, Sourav PalAbstract:Multi-reference coupled cluster methods are established as accurate and efficient tools for describing electronic structure of quasi degenerate states. Recently we have developed multi-reference coupled cluster linear response approach based on the constrained variation method. The method is very general and can describe challenging problems due to the multiple-root nature of effective Hamiltonian. Calculation of response properties for the ionized/electron attached or excited state molecules is a challenging task. With this formulation it is possible to accurately predict the higher order molecular properties of the open shell molecules. In this article we review the response approaches for quasi degenerate cases with emphasis on Fock Space multi-reference coupled cluster method.
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a general formalism of the Fock Space multireference coupled cluster method for investigating molecular electronic resonances
Molecular Physics, 2005Co-Authors: Y Sajeev, Sourav PalAbstract:Electron correlation and relaxation effects play a substantial role in the formation and decay of resonance states. In this paper we formulate a complex absorbing potential combined with the Fock Space multireference coupled cluster method for the correlated calculations of resonance energy and width. This can describe the dynamic and non-dynamic electron correlation efficiently in the ionized or electron attached states.
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adiabatic states of ozone using Fock Space multireference coupled cluster method
Journal of Chemical Physics, 1999Co-Authors: Nayana Vaval, Sourav PalAbstract:In this paper we present the Fock Space multireference coupled cluster theory suitable for calculation of low-lying adiabatically excited or electron attached states. Low-lying adiabatic as well as vertical excited states of ozone are calculated using this theory in singles and doubles approximation. The calculated adiabatic excitation energies are compared with the experimental values. We also report the adiabatic electron affinity value of ozone.
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z vector formalism for the Fock Space multireference coupled cluster method elimination of the response of the highest valence sector amplitudes
Journal of Chemical Physics, 1999Co-Authors: D Ajitha, Sourav PalAbstract:In this paper we present Z-vector formalism for the Fock Space multireference coupled cluster framework. We present detailed equations describing the derivative effective Hamiltonian, where the response amplitudes of the highest Fock sector are eliminated. We discuss the conditions and approximations under which the formalism is possible. We also discuss the implications and comparison with the similar formalism in the single reference framework. The computational advantages and feasibility are also commented upon in this paper.
Nayana Vaval - One of the best experts on this subject based on the ideXlab platform.
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electronic transition dipole moments and dipole oscillator strengths within Fock Space multi reference coupled cluster framework an efficient and novel approach
Journal of Chemical Physics, 2013Co-Authors: Debarati Bhattacharya, Nayana VavalAbstract:Within the Fock-Space multi-reference coupled cluster framework, we have evaluated the electronic transition dipole moments, which determine absorption intensities. These depend on matrix elements between two different wave functions (e.g., ground state to the excited state). We present two different ways, to calculate these transition moments. In the first method, we construct the ground and excited state wave functions with the normal exponential ansatz of Fock-Space coupled cluster method and then calculate the relevant off-diagonal matrix elements. In the second approach, we linearize the exponential form of the wave operator which will generate the left vector, by use of Lagrangian formulation. The right vector is obtained from the exponential ansatz. In order to relate the transition moments to oscillator strengths, excitation energies need to be evaluated. The excitation energies are obtained from the Fock-Space multi-reference framework. The transition dipole moments of the ground to a few excited states, together with the oscillator strengths of a few molecules, are presented.
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effect of triples to dipole moments in Fock Space multireference coupled cluster method
Journal of Chemical Theory and Computation, 2011Co-Authors: Lalitha Ravichandran, Nayana Vaval, Sourav PalAbstract:In this paper, we present the new implementation of partial triples for the dipole moment of doublet radicals in Lagrangian formulation of Fock-Space multireference coupled cluster (Λ-FSMRCC) response method. We have implemented a specific scheme of noniterative triples, in addition to singles and doubles schemes, which accounts for the effects appearing at least at the third order in dipole moments. The method is applied to the ground states of OH, OOH, HCOO, CN, CH, and PO radicals.
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on some aspects of Fock Space multi reference coupled cluster singles and doubles energies and optical properties
2010Co-Authors: Prashant Uday Manohar, Nayana Vaval, Kodagenahalli R Shamasundar, Arijit Bag, Sourav PalAbstract:Multi-reference coupled cluster methods are established as accurate and efficient tools for describing electronic structure of quasi degenerate states. Recently we have developed multi-reference coupled cluster linear response approach based on the constrained variation method. The method is very general and can describe challenging problems due to the multiple-root nature of effective Hamiltonian. Calculation of response properties for the ionized/electron attached or excited state molecules is a challenging task. With this formulation it is possible to accurately predict the higher order molecular properties of the open shell molecules. In this article we review the response approaches for quasi degenerate cases with emphasis on Fock Space multi-reference coupled cluster method.
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adiabatic states of ozone using Fock Space multireference coupled cluster method
Journal of Chemical Physics, 1999Co-Authors: Nayana Vaval, Sourav PalAbstract:In this paper we present the Fock Space multireference coupled cluster theory suitable for calculation of low-lying adiabatically excited or electron attached states. Low-lying adiabatic as well as vertical excited states of ozone are calculated using this theory in singles and doubles approximation. The calculated adiabatic excitation energies are compared with the experimental values. We also report the adiabatic electron affinity value of ozone.
Uzi Kaldor - One of the best experts on this subject based on the ideXlab platform.
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mixed sector intermediate hamiltonian Fock Space coupled cluster approach
Journal of Chemical Physics, 2004Co-Authors: Arie Landau, Ephraim Eliav, Yasuyuki Ishikawa, Uzi KaldorAbstract:An alternative formulation of the intermediate Hamiltonian Fock-Space coupled cluster scheme developed before is presented. The methodological and computational advantages of the new formulation include the possibility of using a model Space with determinants belonging to different Fock-Space sectors. This extends the scope of application of the multireference coupled cluster method, and makes possible the use of quasiclosed shells (e.g., p2, d4) as reference states. Representative applications are described, including electron affinities of group-14 atoms, ionization potentials of group-15 elements, and ionization potentials and excitation energies of silver and gold. Excellent agreement with experiment (a few hundredths of an electronvolt) is obtained, with significant improvement (by a factor of 5-10 for p3 states) over Fock-Space coupled cluster results. Many states not reachable by the Fock-Space approach can now be studied.
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Formulation and implementation of the relativistic Fock-Space coupled cluster method for molecules
The Journal of Chemical Physics, 2001Co-Authors: Lucas Visscher, Ephraim Eliav, Uzi KaldorAbstract:An implementation of the relativistic multireference Fock-Space coupled cluster method is presented which allows simultaneous calculation of potential surfaces for different oxidation states and electronic levels of a molecule, yielding values for spectroscopic constants and transition energies. The method is tested in pilot calculations on the I2 and HgH molecules, and is shown to give a good and balanced description of various electronic states and energies.
Ephraim Eliav - One of the best experts on this subject based on the ideXlab platform.
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diagonal and off diagonal hyperfine structure matrix elements in kcs within the relativistic Fock Space coupled cluster theory
Chemical Physics Letters, 2020Co-Authors: Ephraim Eliav, Alexander V Oleynichenko, Leonid V Skripnikov, A V Zaitsevskii, V M ShabaevAbstract:Abstract The four-component relativistic Fock Space coupled cluster method is used to describe the magnetic hyperfine interaction in low-lying electronic states of the KCs molecule. Both diagonal and off-diagonal matrix elements as functions of the internuclear separation R are calculated within the finite-field scheme. The resulting matrix elements exhibit very weak dependence on R for the separations exceeding 8 A, whereas in the vicinity of the ground-state equilibrium the deviation of molecular HFS matrix elements from the atomic values reaches 15%. The dependence of the computed HFS couplings on the level of core correlation treatment is discussed.
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mixed sector intermediate hamiltonian Fock Space coupled cluster approach
Journal of Chemical Physics, 2004Co-Authors: Arie Landau, Ephraim Eliav, Yasuyuki Ishikawa, Uzi KaldorAbstract:An alternative formulation of the intermediate Hamiltonian Fock-Space coupled cluster scheme developed before is presented. The methodological and computational advantages of the new formulation include the possibility of using a model Space with determinants belonging to different Fock-Space sectors. This extends the scope of application of the multireference coupled cluster method, and makes possible the use of quasiclosed shells (e.g., p2, d4) as reference states. Representative applications are described, including electron affinities of group-14 atoms, ionization potentials of group-15 elements, and ionization potentials and excitation energies of silver and gold. Excellent agreement with experiment (a few hundredths of an electronvolt) is obtained, with significant improvement (by a factor of 5-10 for p3 states) over Fock-Space coupled cluster results. Many states not reachable by the Fock-Space approach can now be studied.
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Formulation and implementation of the relativistic Fock-Space coupled cluster method for molecules
The Journal of Chemical Physics, 2001Co-Authors: Lucas Visscher, Ephraim Eliav, Uzi KaldorAbstract:An implementation of the relativistic multireference Fock-Space coupled cluster method is presented which allows simultaneous calculation of potential surfaces for different oxidation states and electronic levels of a molecule, yielding values for spectroscopic constants and transition energies. The method is tested in pilot calculations on the I2 and HgH molecules, and is shown to give a good and balanced description of various electronic states and energies.
