On the calculation of expectation values and transition matrix elements by coupled cluster method

1994 ◽  
Vol 88 (5) ◽  
pp. 383-388 ◽  
Author(s):  
M. Durga Prasad
Keyword(s):  
Transition Matrix ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Matrix Elements ◽  
Coupled Cluster Method ◽  
Expectation Values ◽  
Transition Matrix Elements

scholarly journals Finite-Field Calculations of Transition Properties by the Fock Space Relativistic Coupled Cluster Method: Transitions between Different Fock Space Sectors

2020 ◽  
Author(s):  
Andrei Zaitsevskii ◽  
Alexander Oleynichenko ◽  
Ephraim Eliav
Keyword(s):  
Finite Field ◽  
Transition Matrix ◽  
Fock Space ◽  
Electronic States ◽  
Radiative Properties ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Matrix Elements ◽  
Transition Dipole ◽  
Transition Matrix Elements

Reliable information on transition matrix elements of various property operators between molecular electronic states is of crucial importance for predicting spectroscopic, electric, magnetic and radiative properties of molecules. The finite-field technique is a simple and rather accurate tool for evaluating transition matrix elements of first-order properties in the frames of the Fock space relativistic coupled cluster approach. We formulate and discuss the extension of this technique to the case of transitions between the electronic states associated with different sectors of the Fock space. Pilot applications to the evaluation of transition dipole moments between the closed-shell-like states (vacuum sector) and those dominated by single excitations of the Fermi vacuum (the $1h1p$ sector) in heavy atoms (Xe, Hg) and simple molecules of heavy element compounds (I${}_2$, TlF) are reported.

scholarly journals Finite-Field Calculations of Transition Properties by the Fock Space Relativistic Coupled Cluster Method: Transitions between Different Fock Space Sectors

Symmetry ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 1845
Author(s):  
Andréi Zaitsevskii ◽  
Alexander V. Oleynichenko ◽  
Ephraim Eliav
Keyword(s):  
Finite Field ◽  
Transition Matrix ◽  
Fock Space ◽  
Electronic States ◽  
Radiative Properties ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Matrix Elements ◽  
Transition Dipole ◽  
Transition Matrix Elements

Reliable information on transition matrix elements of various property operators between molecular electronic states is of crucial importance for predicting spectroscopic, electric, magnetic and radiative properties of molecules. The finite-field technique is a simple and rather accurate tool for evaluating transition matrix elements of first-order properties in the frames of the Fock space relativistic coupled cluster approach. We formulate and discuss the extension of this technique to the case of transitions between the electronic states associated with different sectors of the Fock space. Pilot applications to the evaluation of transition dipole moments between the closed-shell-like states (vacuum sector) and those dominated by single excitations of the Fermi vacuum (the 1h1p sector) in heavy atoms (Xe and Hg) and simple molecules of heavy element compounds (I2 and TlF) are reported.

scholarly journals ODD AND EVEN BEHAVIOR WITH LSUBm APPROXIMATION LEVEL IN HIGH-ORDER COUPLED CLUSTER METHOD (CCM) CALCULATIONS

2008 ◽  
Vol 22 (20) ◽  
pp. 3369-3379 ◽  
Author(s):  
D. J. J. FARNELL ◽  
R. F. BISHOP
Keyword(s):  
Ground State Energy ◽  
Ground State ◽  
State Energy ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Computational Techniques ◽  
Great Success ◽  
Coupled Cluster Method ◽  
Expectation Values ◽  
Sublattice Magnetization

The coupled cluster method (CCM) is a powerful and widely applied technique of modern-day quantum many-body theory. It has been used with great success in order to understand the properties of quantum magnets at zero temperature. This is largely due to the application of computational techniques that allow the method to be applied to high orders of approximation using a localized scheme known as the LSUBm scheme. A hitherto unreported aspect of this scheme is that results for LSUBm expectation values behave in distinctly different ways with odd and even values of m. Here, we consider the behavior of ground-state expectation values of odd and even orders of the CCM LSUBm approximation for unfrustrated spin-half Heisenberg antiferromagnets on the square and honeycomb lattice and the frustrated spin-half Heisenberg antiferromagnet on the triangular lattice. We demonstrate that results for odd and even orders of approximation show qualitatively different behavior for both the ground-state energy and the sublattice magnetization. Indeed, the odd series consistently forms an upper branch of results, and the even series a lower branch with respect to both ground-state energy and sublattice magnetization, for all of the models considered here.

The relativistic coupled-cluster method: transition energies of bismuth and eka-bismuth

1998 ◽  
Vol 94 (1) ◽  
pp. 181-187 ◽  
Author(s):  
EPHRAIM ELIAV ◽  
UZI KALDOR ◽  
YASUYUKI ISHIKAWA
Keyword(s):  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Transition Energies

A Multi-Layer Approach to the Equation of Motion Coupled-Cluster Method for the Electron Affinity

2020 ◽  
Author(s):  
Soumi Haldar ◽  
Achintya Kumar Dutta
Keyword(s):  
Electron Affinity ◽  
Electron Attachment ◽  
Equation Of Motion ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Large Molecules ◽  
Layer Method ◽  
Speed Up ◽  
Attachment Process

We have presented a multi-layer implementation of the equation of motion coupled-cluster method for the electron affinity, based on local and pair natural orbitals. The method gives consistent accuracy for both localized and delocalized anionic states. It results in many fold speedup in computational timing as compared to the canonical and DLPNO based implementation of the EA-EOM-CCSD method. We have also developed an explicit fragment-based approach which can lead to even higher speed-up with little loss in accuracy. The multi-layer method can be used to treat the environmental effect of both bonded and non-bonded nature on the electron attachment process in large molecules.<br>

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