Non-iterative fifth-order triple and quadruple excitation energy corrections in correlated methods

Abstract In critical cases, single-reference correlated methods like coupled-cluster theory or its quadratic CI approximations fail because of the importance of additional highly excited excitations that cannot usually be included, like connected triple and quadruple excitations. Here we present the first, non-iterative method to evaluate the full set of fifth-order corrections to CCSD and QCISD and assess their accuracy compared to full CI for the very sensitive Be 2 curve and other cases.

[1]  Rodney J. Bartlett,et al.  Fifth-Order Many-Body Perturbation Theory and Its Relationship to Various Coupled-Cluster Approaches* , 1986 .

[2]  Krishnan Raghavachari,et al.  An augmented coupled cluster method and its application to the first‐row homonuclear diatomics , 1985 .

[3]  Rodney J. Bartlett,et al.  Molecular Applications of Coupled Cluster and Many-Body Perturbation Methods , 1980 .

[4]  David H. Magers,et al.  Correlated studies of infrared intensities , 1989 .

[5]  R. Bartlett,et al.  Towards a full CCSDT model for electron correlation. CCSDT-n models , 1987 .

[6]  C. Bauschlicher,et al.  Benchmark full configuration-interaction calculations on HF and NH2 , 1986 .

[7]  P. Taylor,et al.  A full CI treatment of the 1A1-3B1 separation in methylene , 1986 .

[8]  Rodney J. Bartlett,et al.  Alternative coupled-cluster ansätze II. The unitary coupled-cluster method , 1989 .

[9]  R. Bartlett,et al.  A study of the Be2 potential curve using the full (CCSDT) coupled‐cluster method: The importance of T4 clusters , 1988 .

[10]  R. Bartlett,et al.  Theoretical study of PO and PO− , 1988 .

[11]  Martin Head-Gordon,et al.  Quadratic configuration interaction. A general technique for determining electron correlation energies , 1987 .

[12]  R. Bartlett,et al.  A full coupled‐cluster singles and doubles model: The inclusion of disconnected triples , 1982 .

[13]  R. Bartlett,et al.  The full CCSDT model for molecular electronic structure , 1987 .

[14]  R. Bartlett,et al.  Fifth‐order many‐body perturbation theory for molecular correlation energies , 1989 .

[15]  C. Bauschlicher,et al.  A full CI treatment of the 1A1,1B1, and 3B1 states of SiH2 , 1987 .

[16]  R. Bartlett,et al.  The equilibrium structure and harmonic vibrational frequencies of ozone: coupled cluster results including triple excitations , 1989 .

[17]  R. Bartlett.  Coupled-cluster approach to molecular structure and spectra: a step toward predictive quantum chemistry , 1989 .

[18]  R. Bartlett,et al.  Coupled-cluster methods that include connected quadruple excitations, T4: CCSDTQ-1 and Q(CCSDT) , 1989 .

[19]  S. J. Cole,et al.  Towards a full CCSDT model for electron correlation , 1985 .

[20]  Rodney J. Bartlett,et al.  The expectation value coupled-cluster method and analytical energy derivatives☆ , 1988 .

[21]  M. Head‐Gordon,et al.  A fifth-order perturbation comparison of electron correlation theories , 1989 .

[22]  R. Bartlett,et al.  A coupled‐cluster method that includes connected quadruple excitations , 1989 .

[23]  N. Handy,et al.  Full CI results for Be2 and (H2)2 in large basis sets , 1983 .

[24]  R. Bartlett,et al.  A coupled cluster approach with triple excitations , 1984 .

[25]  Rodney J. Bartlett,et al.  A multi-reference coupled-cluster method for molecular applications , 1984 .