Journal ArticleDOI
A spin-adapted linear response theory in a coupled-cluster framework for direct calculation of spin-allowed and spin-forbidden transition energies
Somnath Ghosh,Debashis Mukherjee,Subir Bhattacharyya +2 more
- Vol. 72, Iss: 1, pp 161-176
TLDR
In this paper, a spin-adapted linear response theory in a coupled-cluster framework was proposed to calculate the spin-allowed and spin-forbidden transition energies from a single methodology.Abstract:
In this paper, we have spin-adapted our recently formulated linear response theory in a coupled-cluster framework. This allows us to calculate directly both the spin-allowed and the spin-forbidden transition energies from a single methodology. We have introduced rank-zero and rank-one spin operators to construct excitation operators for singlet-singlet and singlet-triplet transitions respectively and utilised the graphical methods of spin algebra to integrate the spin variables. It has been shown how a suitable parameterisation of the reduced Hugenholtz matrix elements of the excitation operator in terms of Goldstone matrix elements makes the resulting system of equations simple, compact and suitable for computer implementation. A pilot calculation has been performed to test the applicability of the theory.read more
Citations
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Journal ArticleDOI
Spin-adapted open-shell random phase approximation and time-dependent density functional theory. I. Theory.
Zhendong Li,Wenjian Liu +1 more
TL;DR: A tensor-coupling scheme that invokes all the components of a reference multiplet rather than increases the excitation ranks is proposed, and it is shown that spin-contaminated spin-flip configuration interaction approaches can easily be spin-adapted via the Tensor-Coupled scheme.
Book ChapterDOI
Algebraic Approach to Coupled Cluster Theory
TL;DR: The importance of size-extensivity in finite atomic and molecular systems was first recognized by Primas (1965), even though the term itself was coined and employed only later by Pople et al..
Journal ArticleDOI
Benchmarking second order methods for the calculation of vertical electronic excitation energies: valence and Rydberg states in polycyclic aromatic hydrocarbons.
TL;DR: The performance of the six second order linear response methods RPA(D), SopPA, SOPPA(CCSD), CIS(D, CC2), CC2, and CCSD, which include either noniterative or iterative doubles contributions, has been studied in calculations of vertical excitation energies.
Journal ArticleDOI
Triplet excitation energies in the coupled cluster singles and doubles model using an explicit triplet spin coupled excitation space
TL;DR: In this article, triplet excitation spectrum of benzene is calculated using from 147 to 432 basis functions using an integral direct approach and an explicit spin coupled triplet space, and compared with experimental and other theoretical values.
Journal ArticleDOI
Molecular applications of open-shell coupled cluster theory for energy difference calculations: ionization and auger spectra of F2
TL;DR: The first ab initio molecular applications of the open-shell coupled cluster (CC) method for direct calculation of energy differences are reported in this article, starting from the zero-valence ground-state problem, various one-, two-, ⋯ m -valence problems are hierarchically generated.
References
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Journal ArticleDOI
On the Correlation Problem in Atomic and Molecular Systems. Calculation of Wavefunction Components in Ursell-Type Expansion Using Quantum-Field Theoretical Methods
TL;DR: In this article, a method for the calculation of the matrix elements of the logarithm of an operator which gives the exact wavefunction when operating on the wavefunction in the one-electron approximation is proposed.
Journal ArticleDOI
The iterative calculation of a few of the lowest eigenvalues and corresponding eigenvectors of large real-symmetric matrices
Journal ArticleDOI
A response-function approach to the direct calculation of the transition-energy in a multiple-cluster expansion formalism
TL;DR: In this paper, a response function approach to the direct determination of transition energy in a multiple-cluster expansion formalism has been developed, in a way reminiscent of the Fourier-transformed version of a response-function theory.
Journal ArticleDOI
Correlation problem in open-shell atoms and molecules
TL;DR: In this article, a non-perturbative approach to the calculation of correlation energies of open-shell systems is presented, which utilizes an Ursell-type expansion about a multi-determinant starting wave function.