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Majee K, Chakraborty S, Mukhopadhyay T, Nayak MK, Dutta AK. A reduced cost four-component relativistic unitary coupled cluster method for atoms and molecules. J Chem Phys 2024; 161:034101. [PMID: 39007370 DOI: 10.1063/5.0207091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Accepted: 06/12/2024] [Indexed: 07/16/2024] Open
Abstract
We present a four-component relativistic unitary coupled cluster method for atoms and molecules. We have used commutator-based non-perturbative approximation using the "Bernoulli expansion" to derive an approximation to the relativistic unitary coupled cluster method. The performance of the full quadratic unitary coupled-cluster singles and doubles method (qUCCSD), as well as a perturbative approximation variant (UCC3), has been reported for both energies and properties. It can be seen that both methods give results comparable to those of the standard relativistic coupled cluster method. The qUCCSD method shows better agreement with experimental results due to the better inclusion of relaxation effects. The relativistic UCC3 and qUCCSD methods can simulate the spin-forbidden transition with easy access to transition properties. A natural spinor-based scheme to reduce the computational cost of relativistic UCC3 and qUCCSD methods has been discussed.
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Affiliation(s)
- Kamal Majee
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Sudipta Chakraborty
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Tamoghna Mukhopadhyay
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Malaya K Nayak
- Theoretical Chemistry Section, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
- Homi Bhabha National Institute, BARC Training School Complex, Anushakti Nagar, Mumbai 400094, India
| | - Achintya Kumar Dutta
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
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Skripnikov LV, Oleynichenko AV, Zaitsevskii A, Mosyagin NS, Athanasakis-Kaklamanakis M, Au M, Neyens G. Ab initio study of electronic states and radiative properties of the AcF molecule. J Chem Phys 2023; 159:124301. [PMID: 38127371 DOI: 10.1063/5.0159888] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Accepted: 09/01/2023] [Indexed: 12/23/2023] Open
Abstract
Relativistic coupled-cluster calculations of the ionization potential, dissociation energy, and excited electronic states under 35 000 cm-1 are presented for the actinium monofluoride (AcF) molecule. The ionization potential is calculated to be IPe = 48 866 cm-1, and the ground state is confirmed to be a closed-shell singlet and thus strongly sensitive to the T,P-violating nuclear Schiff moment of the Ac nucleus. Radiative properties and transition dipole moments from the ground state are identified for several excited states, achieving a mean uncertainty estimate of ∼450 cm-1 for the excitation energies. For higher-lying states that are not directly accessible from the ground state, possible two-step excitation pathways are proposed. The calculated branching ratios and Franck-Condon factors are used to investigate the suitability of AcF for direct laser cooling. The lifetime of the metastable (1)3Δ1 state, which can be used in experimental searches of the electric dipole moment of the electron, is estimated to be of order 1 ms.
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Affiliation(s)
- Leonid V Skripnikov
- Petersburg Nuclear Physics Institute named by B. P. Konstantinov of National Research Center "Kurchatov Institute" (NRC "Kurchatov Institute" - PNPI), 1 Orlova roscha, Gatchina, 188300 Leningrad region, Russia
- Saint Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia
| | - Alexander V Oleynichenko
- Petersburg Nuclear Physics Institute named by B. P. Konstantinov of National Research Center "Kurchatov Institute" (NRC "Kurchatov Institute" - PNPI), 1 Orlova roscha, Gatchina, 188300 Leningrad region, Russia
| | - Andréi Zaitsevskii
- Petersburg Nuclear Physics Institute named by B. P. Konstantinov of National Research Center "Kurchatov Institute" (NRC "Kurchatov Institute" - PNPI), 1 Orlova roscha, Gatchina, 188300 Leningrad region, Russia
- Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie gory 1/3, Moscow 119991, Russia
| | - Nikolai S Mosyagin
- Petersburg Nuclear Physics Institute named by B. P. Konstantinov of National Research Center "Kurchatov Institute" (NRC "Kurchatov Institute" - PNPI), 1 Orlova roscha, Gatchina, 188300 Leningrad region, Russia
| | - Michail Athanasakis-Kaklamanakis
- Experimental Physics Department, CERN, CH-1211 Geneva 23, Switzerland
- KU Leuven, Instituut voor Kern- en Stralingsfysica, B-3001 Leuven, Belgium
| | - Mia Au
- Systems Department, CERN, CH-1211 Geneva 23, Switzerland
| | - Gerda Neyens
- KU Leuven, Instituut voor Kern- en Stralingsfysica, B-3001 Leuven, Belgium
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Isaev T, Makinskii D, Zaitsevskii A. Radium-containing molecular cations amenable for laser cooling. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2022.140078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Zaitsevskii A, Skripnikov LV, Mosyagin NS, Isaev T, Berger R, Breier AA, Giesen TF. Accurate ab initio calculations of RaF electronic structure appeal to more laser-spectroscopical measurements. J Chem Phys 2022; 156:044306. [PMID: 35105071 DOI: 10.1063/5.0079618] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Recently, a breakthrough has been achieved in laser-spectroscopic studies of short-lived radioactive compounds with the first measurements of the radium monofluoride molecule (RaF) UV/vis spectra. We report results from high-accuracy ab initio calculations of the RaF electronic structure for ground and low-lying excited electronic states. Two different methods agree excellently with experimental excitation energies from the electronic ground state to the 2Π1/2 and 2Π3/2 states, but lead consistently and unambiguously to deviations from experimental-based adiabatic transition energy estimates for the 2Σ1/2 excited electronic state, and show that more measurements are needed to clarify spectroscopic assignment of the 2Δ state.
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Affiliation(s)
- Andrei Zaitsevskii
- NRC "Kurchatov Institute"-PNPI, Orlova Roscha, 1, 188300 Gatchina, Russia
| | | | - Nikolai S Mosyagin
- NRC "Kurchatov Institute"-PNPI, Orlova Roscha, 1, 188300 Gatchina, Russia
| | - Timur Isaev
- NRC "Kurchatov Institute"-PNPI, Orlova Roscha, 1, 188300 Gatchina, Russia
| | - Robert Berger
- Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str 4, 35032 Marburg, Germany
| | - Alexander A Breier
- Laboratory for Astrophysics, Institute of Physics, University of Kassel, 34132 Kassel, Germany
| | - Thomas F Giesen
- Laboratory for Astrophysics, Institute of Physics, University of Kassel, 34132 Kassel, Germany
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Osika Y, Shundalau M. Fock-space relativistic coupled cluster study on the RaF molecule promising for the laser cooling. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022; 264:120274. [PMID: 34438114 DOI: 10.1016/j.saa.2021.120274] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 07/05/2021] [Accepted: 08/08/2021] [Indexed: 06/13/2023]
Abstract
The potential energy curves of the ground and five low-lying excited terms of the RaF molecule are calculated using the Fock-space relativistic coupled theory. The electronic term energies, equilibrium internuclear distances, transition and permanent dipole moments, sequences of vibrational energies, harmonic vibrational frequencies, Franck-Condon factors, and radiative lifetimes are predicted. The calculated spectroscopic constants are in good agreement with the available theoretical and experimental data. The scheme for the direct laser cooling involving the first excited A2П1/2 state is proposed. The data obtained in this study suggests the A2П1/2 → X2Σ+ channel in the RaF molecule is the almost ideal case for direct laser cooling. It is quite possible that the effective cooling scheme for the RaF molecule can be realized using only one pump laser.
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Affiliation(s)
- Yuliya Osika
- Faculty of Physics, Belarusian State University, 4 Nezaležnaści Ave., Minsk 220030, Belarus
| | - Maksim Shundalau
- Faculty of Physics, Belarusian State University, 4 Nezaležnaści Ave., Minsk 220030, Belarus.
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Haldar S, Dutta AK. An efficient Fock space multi-reference coupled cluster method based on natural orbitals: Theory, implementation, and benchmark. J Chem Phys 2021; 155:014105. [PMID: 34241374 DOI: 10.1063/5.0054171] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present a natural orbital-based implementation of the intermediate Hamiltonian Fock space coupled-cluster method for the (1, 1) sector of Fock space. The use of natural orbitals significantly reduces the computational cost and can automatically choose an appropriate set of active orbitals. The new method retains the charge transfer separability of the original intermediate Hamiltonian Fock space coupled-cluster method and gives excellent performance for valence, Rydberg, and charge-transfer excited states. It offers significant computational advantages over the popular equation of motion coupled cluster method for excited states dominated by single excitations.
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Affiliation(s)
- Soumi Haldar
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Achintya Kumar Dutta
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
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