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
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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
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Multireference coupled-cluster methods using an incomplete model space: Application to ionization potentials and excitation energies of formaldehyde
TL;DR: In this paper, a multireference coupled-cluster method using an incomplete model space is applied to the direct calculation of the difference energies of formaldehyde, which is made of a reference space composed of particle-hole excited configurations built from a set of active orbitals.
Journal ArticleDOI
Second order many-body perturbation approximations to the Coupled Cluster Green's Function.
Marcel Nooijen,J.G. Snijders +1 more
TL;DR: In this paper, the authors investigated the accuracy that can be obtained if the CCSD coefficients are replaced by their MBPT(2) analogs and discussed some additional diagonal approximations that might prove especially useful in polymer calculations, and compared with traditional Green's function calculations based on a second order approximation to the irreducible self-energy.
Journal ArticleDOI
A non-Dyson third-order approximation scheme for the electron propagator
TL;DR: An efficient third-order propagator method to compute ionization potentials and electron affinities of atoms and molecules is presented in this paper, which is based on the algebraic diagrammatic construction (ADC) representing a specific reformulation of the diagrammatic perturbation series of the electron propagator G(ω) in contrast with previous approximation schemes, relying on the Dyson equation and approximations for the self-energy part.
Journal ArticleDOI
A consistent third-order propagator method for electronic excitation
TL;DR: In this article, a third-order algebraic-diagrammatic construction (ADC(3) method for direct computation of electronic excitation energies and transition moments is presented, based on a specific reformulation of the diagrammatic perturbation expansion for the polarization propagator.
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.
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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.