Use of recursively generated intermediates in state selective multireference coupled‐cluster method: A numerical example

The present work represents the first attempt to utilize the idea of recursively generated intermediates (RGI) in the framework of the state‐selective multi‐reference coupled‐cluster method truncated at triple excitations [SS CCSD(T)]. The expressions for stepwise generation of intermediates are so structured that the spin and point symmetry simplifications can be easily applied during computation. Suitable modifications in SS CCSD(T) equations are introduced to allow for optional quasilinearization of nonlinear terms in difficult convergence situations. The computational code is, as expected, much faster than the SS CCSD(T) code without RGI adaptation. This has been numerically demonstrated by potential energy surface (PES) calculation of the HF molecule using a double zeta basis.

[1]  P. Piecuch,et al.  Improved computational strategy for the state‐selective coupled‐cluster theory with semi‐internal triexcited clusters: Potential energy surface of the HF molecule , 1995 .

[2]  P. Piecuch,et al.  Solving the single‐reference coupled‐cluster equations involving highly excited clusters in quasidegenerate situations , 1994 .

[3]  Ludwik Adamowicz,et al.  STATE-SELECTIVE MULTIREFERENCE COUPLED-CLUSTER THEORY EMPLOYING THE SINGLE-REFERENCE FORMALISM : IMPLEMENTATION AND APPLICATION TO THE H8 MODEL SYSTEM , 1994 .

[4]  Ludwik Adamowicz,et al.  A state-selective multireference coupled-cluster theory employing the single-reference formalism , 1993 .

[5]  R. Bartlett,et al.  The coupled‐cluster single, double, triple, and quadruple excitation method , 1992 .

[6]  Ludwik Adamowicz,et al.  The implementation of the multireference coupled‐cluster method based on the single‐reference formalism , 1992 .

[7]  N. Oliphant,et al.  Converging the single-reference coupled-cluster equations , 1992 .

[8]  R. Bartlett,et al.  Recursive intermediate factorization and complete computational linearization of the coupled-cluster single, double, triple, and quadruple excitation equations , 1991 .

[9]  John D. Watts,et al.  Non-iterative fifth-order triple and quadruple excitation energy corrections in correlated methods , 1990 .

[10]  J. Paldus,et al.  Valence universal exponential ansatz and the cluster structure of multireference configuration interaction wave function , 1989 .

[11]  Josef Paldus,et al.  Spin‐adapted multireference coupled‐cluster approach: Linear approximation for two closed‐shell‐type reference configurations , 1988 .

[12]  Rodney J. Bartlett,et al.  The reduced linear equation method in coupled cluster theory. , 1981 .

[13]  T. H. Dunning.  Gaussian Basis Functions for Use in Molecular Calculations. III. Contraction of (10s6p) Atomic Basis Sets for the First‐Row Atoms , 1970 .

[14]  J. Cizek.  On the Correlation Problem in Atomic and Molecular Systems. Calculation of Wavefunction Components in Ursell-Type Expansion Using Quantum-Field Theoretical Methods , 1966 .