Multi-reference Fock space coupled-cluster method in the intermediate Hamiltonian formulation for potential energy surfaces

2011 ◽  
Vol 135 (4) ◽  
pp. 044121 ◽  
Author(s):  
Monika Musiał ◽  
Rodney J. Bartlett
Keyword(s):  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Fock Space ◽  
Hamiltonian Formulation ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Energy Surfaces

The Fock-Space Coupled-Cluster Method in the Calculation of Excited State Properties

2005 ◽  
Vol 70 (6) ◽  
pp. 811-825 ◽  
Author(s):  
Monika Musiał ◽  
Leszek Meissner
Keyword(s):  
Experimental Data ◽  
Excited States ◽  
Fock Space ◽  
Hamiltonian Formulation ◽  
Basis Sets ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Excitation Energies ◽  
Equilibrium Geometries

Our recently developed intermediate Hamiltonian Fock-space coupled-cluster (FS-CC) method with singles and doubles is applied to calculation of equilibrium geometries, harmonic frequencies and adiabatic excitation energies for some excited states of N2 and CO. Due to the intermediate Hamiltonian formulation, which provides a robust computational scheme for solving the FS-CC equations, and the efficient factorization strategy, relatively large basis sets and reference spaces are employed permitting a comparison of calculated properties with experimental data.

Effective Hamiltonian and Intermediate Hamiltonian Formulations of the Fock-Space Coupled-Cluster Method

2003 ◽  
Vol 68 (1) ◽  
pp. 105-138 ◽  
Author(s):  
Leszek Meissner ◽  
JarosłaW Gryniaków
Keyword(s):  
Schrödinger Equation ◽  
Schrodinger Equation ◽  
Fock Space ◽  
Hamiltonian Formulation ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Effective Hamiltonian ◽  
Coupled Cluster Method ◽  
Effective Version ◽  
Reference Methods

Various aspects of the effective Hamiltonian and intermediate Hamiltonian formulations are discussed in the context of the Fock-space coupled-cluster method. Problems that occur when single-reference methods of solving the Schrödinger equation need to be generalized to the multireference (MR) cases are pointed out. These problems make the generalization nontrivial, especially in the case of the most powerful coupled-cluster (CC) method. It is shown how some specific features of one of the basic MR-CC schemes, the Fock-space CC method, can be used to obtain a simple, yet very effective version of the method. This requires, however, switching from the effective Hamiltonian to the intermediate Hamiltonian formulation. The intermediate Hamiltonian version of the Fock-space CC method is discussed in detail and all its advantages over the standard one are emphasized.

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