Multireference State-Specific Coupled-Cluster Theory and Multiconfigurationality Index. BH Dissociation

2005 ◽  
Vol 70 (7) ◽  
pp. 1017-1033 ◽  
Author(s):  
Vladimir V. Ivanov ◽  
Ludwik Adamowicz ◽  
Dmitry I. Lyakh
Keyword(s):  
Wave Function ◽  
Numerical Results ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Computer Aided

Multiconfigurationality index calculated for the coupled-cluster wave function based on an algorithm developed using a computer-aided generation approach is applied to analyze the multireference state-specific coupled-cluster method with the CAS reference (i.e. the so called the CAS(n,m)CCSD approach). The numerical results concern dissociation of the BH molecule where at larger displacement from the equilibrium significant quasi-degeneracy arises. The analysis shows that the CAS(n,m)CCSD approach performs very well in such a situation.

Time-Independent Coupled-Cluster Theory of the Polarization Propagator

2005 ◽  
Vol 70 (8) ◽  
pp. 1109-1132 ◽  
Author(s):  
Robert Moszynski ◽  
Piotr S. Żuchowski ◽  
Bogumił Jeziorski
Keyword(s):  
Order Term ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Cluster Approach ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Polarization Propagator ◽  
Apparent Correlation ◽  
Moller Plesset ◽  
New Formulation

A novel, time-independent formulation of the coupled-cluster theory of the polarization propagator is presented. This formulation, unlike the equation-of-motion coupled-cluster approach, is fully size-extensive and, unlike the conventional time-dependent coupled-cluster method, is manifestly Hermitian, which guarantees that the polarization propagator is always real for purely imaginary frequencies and that the resulting polarizabilities exhibit time-reversal symmetry (are even functions of frequency) for purely real or purely imaginary perturbations. This new formulation is used to derive compact expressions for the three leading terms in the Møller-Plesset expansion for the polarization propagator. The true and apparent correlation contributions to the second-order term are analyzed and separated at the operator level. Explicit equations for the polarization propagator at the non-perturbative, singles and doubles level (CCSD) are presented.

Electronic Spectra and Ionization Potentials of Halogen Oxides Using the Fock Space Coupled-Cluster Method

2005 ◽  
Vol 70 (7) ◽  
pp. 851-863 ◽  
Author(s):  
Nayana Vaval ◽  
Prashant Manohar ◽  
Sourav Pal
Keyword(s):  
Excited States ◽  
Fock Space ◽  
Ionization Potentials ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Excitation Energies ◽  
Coupled Cluster Theory ◽  
Vertical Detachment Energy ◽  
Halogen Oxides

The ionization potentials and excitation energies of halogen monoxides and dihalogen oxides are studied using fully size-extensive Fock space version of multi-reference coupled-cluster theory. The low-lying excited states of ClO-, FO-, Cl2O and F2O are obtained along with the ionization spectra of Cl2O and F2O. The adiabatic electron affinity of ClO, FO and the vertical detachment energy of ClO- and FO- are also presented.

TICC2 STATE-DEPENDENT CORRELATIONS IN NUCLEI

2003 ◽  
Vol 17 (28) ◽  
pp. 5203-5207 ◽  
Author(s):  
I. MOLINER
Keyword(s):  
Wave Function ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coordinate Space ◽  
Coupled Cluster Method ◽  
State Dependent ◽  
Higher Order Terms ◽  
Finite Nuclei ◽  
Ground State Energies

We use the TICC2, a translationally invariant reformulation of the coupled cluster method (CCM) at the sub(2) level, to study finite nuclei within the p-shell. These nuclei were previously studied with the linearised TICI2 wave function, but the role of the higher order terms had not been discussed for nuclei. We shall include the quadratic terms of the wave function within a coordinate-space implementation of the method, and consider state-dependent correlations with the same structure as the semi-realistic interactions used. Using CCM techniques and gaussian expansions we compute the ground-state energies of these nuclei.

COUPLED CLUSTER EXPANSIONS FOR (2 + 1) DIMENSIONAL U(1) LATTICE GAUGE THEORY WITH IMPROVED HAMILTONIAN

2000 ◽  
Vol 15 (11n12) ◽  
pp. 737-745 ◽  
Author(s):  
XI-YAN FANG ◽  
SHUO-HONG GUO ◽  
JIN-MING LIU
Keyword(s):  
Wave Function ◽  
Gauge Theory ◽  
Lattice Gauge Theory ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Cluster Expansions ◽  
Lattice Gauge ◽  
Seventh Order

Using coupled cluster method, we calculate the vacuum wave function and the mass gaps of (2 + 1)-dimensional U(1) lattice gauge theory with improved Hamiltonian up to the seventh order. The results are compared with those from the unimproved Hamiltonian.

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