Spectroscopic investigations on the HCl(X2 Π) ion using coupled-cluster theory in combination with the correlation-consistent quintuple basis set augmented with diffuse functions

2009 ◽  
Vol 110 (8) ◽  
pp. 1481-1488
Author(s):  
De-Heng Shi ◽  
Jin-Ping Zhang ◽  
Jin-Feng Sun ◽  
Hui Liu ◽  
Yu-Fang Liu ◽  
...  
Keyword(s):  
Basis Set ◽  
Coupled Cluster ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Spectroscopic Investigations ◽  
Correlation Consistent

A Case Study of State-Specific and State-Averaged Brueckner Equation-of-Motion Coupled-Cluster Theory: The Ionic-Covalent Avoided Crossing in Lithium Fluoride

2005 ◽  
Vol 70 (8) ◽  
pp. 1082-1108 ◽  
Author(s):  
Marcel Nooijen ◽  
K. R. Shamasundar
Keyword(s):  
Molecular System ◽  
Solution Process ◽  
Iterative Solution ◽  
Equation Of Motion ◽  
The State ◽  
Basis Set ◽  
Coupled Cluster ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Avoided Crossing

State-specific Brueckner equation-of-motion coupled-cluster theory (SS-B-EOMCC) is summarized, which can be considered an internally contracted version of a state-selective multireference coupled-cluster theory, which, however, is not entirely size-consistent. The method is applicable to general multireference problems, adheres to the space and spin symmetries of the molecular system, is straightforwardly extended to a state-averaged version, and has an associated perturbative variant which yields results close to the full coupled-cluster treatment. A key strength is that Brueckner orbitals are used, such that orbitals are optimized in the presence of dynamic correlation. A number of variations on the theme of SS-EOMCC is applied to study the ionic-covalent avoided crossing in LiF in a 6-311++G(3df,3pd) basis set. While reasonable results are obtained at the state-averaged level, the iterative solution process does not consistently converge for SS-EOMCC, due to the non-Hermiticity of the transformed Hamiltonian which may yield complex eigenvalues upon truncated diagonalization. This leads to an irrevocable breakdown of the state-specific EOMCC approach. We indicate some future directions that can resolve some of the problems with the SS-EOMCC methodology, as revealed by the demanding test case of the LiF potential energy curves.

scholarly journals Gas phase RDX decomposition pathways using coupled cluster theory

2016 ◽  
Vol 18 (37) ◽  
pp. 26069-26077 ◽  
Author(s):  
Robert W. Molt ◽  
Thomas Watson ◽  
Alexandre P. Bazanté ◽  
Rodney J. Bartlett ◽  
Nigel G. J. Richards
Keyword(s):  
Free Energy ◽  
Gas Phase ◽  
Basis Set ◽  
Coupled Cluster ◽  
Energy Barriers ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Complete Basis ◽  
Decomposition Mechanisms ◽  
Complete Basis Set

Electronic and free energy barriers for a series of gas-phase RDX decomposition mechanisms have been obtain using coupled cluster singles, doubles, and perturbative triples with complete basis set (CCSD(T)/CBS) electronic energies for MBPT(2)/cc-pVTZ structures.

Frozen Natural Orbitals: Systematic Basis Set Truncation for Coupled-Cluster Theory

2005 ◽  
Vol 70 (6) ◽  
pp. 837-850 ◽  
Author(s):  
Andrew G. Taube ◽  
Rodney J. Bartlett
Keyword(s):  
Small Molecules ◽  
Potential Energy Surfaces ◽  
Equilibrium Structure ◽  
Virtual Space ◽  
Basis Set ◽  
Coupled Cluster ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Equilibrium Structures ◽  
Energy Surfaces

The method of frozen natural orbital (FNO) basis set truncation for coupled-cluster theory is described. Numerical comparisons of the FNO potential energy surfaces of a group of small molecules at the CCSD(T) level in DZP, cc-pVTZ, cc-pVQZ bases show that truncation of up to 50% of the virtual space yields CC correlation energies that are accurate to 90 or 95% when added to the full MBPT(2) basis result. The FNO truncation method is also applied to dimethylnitramine (DMNA): both the equilibrium structure and dimer interactions, yielding results at the CCSD(T) level in both a DZP and cc-pVTZ basis set that agree with literature values. CCSD(T) calculations at two possible equilibrium structures of 1,3,5-trinitrohexahydro-1,3,5-triazine (RDX) in a truncated DZP basis are also reported.

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