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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The equation-of-motion coupled-cluster method: Excitation energies of Be and CO
TL;DR: In this paper, an equation of motion coupled-cluster (EOM-CC) method for the calculation of excitation energies is presented, which is based upon representing an excited state as an excitation from a ground state and the excitation energy is obtained by solving a non-Hermitian eigenvalue problem.
Journal ArticleDOI
A linear response, coupled‐cluster theory for excitation energy
Hideo Sekino,Rodney J. Bartlett +1 more
TL;DR: In this paper, expressions for static and dynamic properties in coupled-cluster (CC) theory are derived using diagrammatic techniques and shown how consideration of orbital relaxation effects in the theory introduces higher-order correlation effects.
Journal ArticleDOI
Equation of motion coupled cluster method for electron attachment
TL;DR: The electron attachment equation of motion coupled cluster (EA•EOMCC) method is derived in this paper, which enables determination of the various bound states of an (N+1)-electron system and the corresponding energy eigenvalues relative to the energy of an N•electron CCSD reference state.
Journal ArticleDOI
On the connectivity criteria in the open-shell coupled-cluster theory for general model spaces
TL;DR: In this article, the authors study the open-shell coupled-cluster theories and examine the current theoretical status regarding the existence or non-existence of a linked-clusters theorem, ensuring the connectedness of the cluster amplitudes and the effective Hamiltonian.
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A critical assessment of coupled cluster method in quantum chemistry
Josef Paldus,Xiangzhu Li +1 more
References
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Journal ArticleDOI
Applications of a non-perturbative many-body formalism to general open-shell atomic and molecular problems: calculation of the ground and the lowest π-π* singlet and triplet energies and the first ionization potential of trans-butadiene
TL;DR: In this article, the authors explore the feasibility of widening the scope of the nonperturbative open-shell many-body formalism, which utilizes an Ursell type of cluster expansion about certain starting wavefunctions spanning a model space.
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Theory of electron affinities of small molecules
Jack Simons,Wesley D. Smith +1 more
TL;DR: In this paper, a physically clear and computationally tractable theory of molecular electron affinities was derived, based on the equations of motion (EoM) method, which has been successfully applied to the prediction of electronic excitation energies.
Journal ArticleDOI
Nonempirical Calculations on Excited States: The Ethylene Molecule
Thom H. Dunning,Vincent McKoy +1 more
TL;DR: In this article, a series of nonempirical calculations are reported on the excited states of the ethylene molecule using a recent minimum basis set LCAO MO SCF wavefunction.
Journal ArticleDOI
Correlation problems in atomic and molecular systems. V. Spin‐adapted coupled cluster many‐electron theory
TL;DR: In this article, the graphical techniques of spin algebras are combined with a diagrammatic approach based on the time independent Wick theorem to yield the spin-adapted form of the coupled cluster theory.
Journal ArticleDOI
A generalization of the Davidson's method to large nonsymmetric eigenvalue problems
Kimihiko Hirao,H. Nakatsuji +1 more
TL;DR: The Davidson's algorithm for solving large symmetric matrices is generalized to nonsymmetric cases and can be expected to converge particularly well for the eigenvalue whose eigenvector has a desired structure.