Gradients coupled-cluster theory

A superior method for the calculation of excited-state PE surfaces is CC2, which is a simplified and computationally efficient variant of coupled-cluster theory with single and double excitations [22], CC2 can be considered as the equivalent of MP2 for excited electronic states. Efficient implementations of CC2 with density fitting [23] and analytic gradients [24] allow reaction path calculations for rather large systems. Being a singlereference method, CC2 fails in the vicinity of conical intersections of excited states with the electronic ground state. 

Tel. 904-392-1597, fax. 904-392-8722, e-mail aces2 qtp.ufl.edu Ab initio molecular orbital code specializing in the evaluation of the correlation energy using many-body perturbation theory and coupled-cluster theory. Analytic gradients of the energy available at MBPT(2), MBPT(3), MBPT(4), and CC levels for restricted and unrestricted Hartree-Fock reference functions. MBPT(2) and CC gradients. Also available for ROHE reference functions. UNIX workstations. 

Analytical Gradient Evaluation in Coupled-Cluster Theory. 

M. R. Hoffmann and J. Simons, Chem. Phys. Lett., 142, 451 (1987). Analytical Energy Gradients for a Unitary Coupled-Cluster Theory. 

A version of Coupled Cluster theory for use in the calculation of linear response functions (LRCCSD) has been developed by Piecuch et a/.135 and applied to the case of ammonia where the dipole and parallel polarizablity has been calculated as a function of the symmetric stretch and inversion internal coordinates. Coriani et a/.136 have also used CCSD response theory to calculate the electric-field-gradient induced birefringence in H2, N2, C2H2 and CH4. 

At first, aU these methods were developed for closed-shell systems only. Later research in this area was directed towards local methods for open-shell systems and excited states, local triples corrections beyond (T) (triples included in coupled cluster iterations), [138], local energy gradients for geometry optimizations of large molecules [139], combination of the local correlation method with explicitly correlated wavefunctions. It is evident from the discussion that these local 0 N) methods open the applications of coupled-cluster theory to entirely new classes of molecules, which were far ont-of-scope for such an accurate treatment before. Possible applications lie, for example, in the determination of the thermochemistry of reactions involving... 

Basis Sets Correlation Consistent Sets Benchmark Studies on Small Molecules Coupled-cluster Theory Gradient Theory M0ller-Plesset Perturbation Theory NMR Chemical Shift Computation Ab Initio Spin Contamination Symmetry in Chemistry. 

Basis Sets Correlation Consistent Sets Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Configuration Interaction Coupled-cluster Theory Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field G2 Theory Geometry Optimization 1 Gradient Theory Inter-molecular Interactions by Perturbation Theory Molecular Magnetic Properties NMR Chemical Shift Computation Ab Initio NMR Chemical Shift Computation Structural Applications Self-consistent Reaction Field Methods Spin Contamination. 

Schwerdtfeger, P., Bast, R., Gerry, M.C.L., Jacob, C.R., Jansen, M., Kelld, V., Mudring, A.V., Sadlej, A.J., Saue, T, Sdhnel, T. and Wagner, F.E. (2005) The quadrupole moment of the 3 /2 nuclear groimd state of Au from electric field gradient relativistic coupled cluster and density functional theory of small molecules and the solid slide. Journal of Chemical Physics, 122,124317-1-124317-9. 

Stanton JF (1993) Many-body methods for excited state potential energy surfaces I. General theory of energy gradients for the equation-of-motion coupled-cluster method. J Chem Phys 99 8840-8847. 

R. J. Bartlett, in Geometrical Derivatives of Energy Surfaces and Molecular Properties, P. Jorgensen and J. Simons, Eds., D. Reidel, Dordrecht, 1986, pp. 35-61. Analytic Evaluation of Gradients in Coupled-Cluster and Many-Body Perturbation Theory. 

G. Fitzgerald, R. J. Harrison, and R. J. Bartlett,/. Chem. Phys., 85, 5143 (1986). Analytic Energy Gradients for General Coupled-Cluster Methods and Fourth-Order Many-Body Perturbation Theory. 

A. C. Scheiner, G. E. Scuseria, J. E. Rice, T. J. Lee, and H. F. Schaefer, /. Chem. Phys., 87, 5361 (1987). Analytic Evaluation of Energy Gradients for the Single and Double Excitation Coupled Cluster (CCSD) Wave Function Theory and Application. 

State Potential Energy Surfaces. I. General Theory of Energy Gradients for the Equation-of-Motion Coupled-Cluster Method. 

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