CC-R12, a correlation cusp corrected coupled-cluster method with a pilot application to the Be2 potential curve

Abstract The concept of wavefunctions with linear r 12 terms is combined with the coupled-cluster Ansatz at the CCSD and CCSD[T] (formerly CCSD+T(CSSD)) levels. Difficult integrals are voided by means of completeness insertations in the “standard approximation”. A new integral package is used and the “orbital-invariant” formalism is implemented. Applications to the Be atom and the Be 2 molecule on the CCSD and CCSD[T] levels are described. With r 12 terms the convergence to the basis set limit is much faster than without these.

[1]  H. Monkhorst,et al.  Random tempering of Gaussian‐type geminals. III. Coupled pair calculations on lithium hydride and beryllium , 1988 .

[2]  N. Handy,et al.  The binding energies of small Be clusters , 1986 .

[3]  Werner Kutzelnigg,et al.  Rates of convergence of the partial‐wave expansions of atomic correlation energies , 1992 .

[4]  W. Kutzelnigg,et al.  Møller-plesset calculations taking care of the correlation CUSP , 1987 .

[5]  G. A. Petersson,et al.  A complete basis set model chemistry. I. The total energies of closed‐shell atoms and hydrides of the first‐row elements , 1988 .

[6]  Wim Klopper,et al.  Orbital-invariant formulation of the MP2-R12 method , 1991 .

[7]  Werner Kutzelnigg,et al.  Quantum chemistry in Fock space. III. Particle‐hole formalism , 1984 .

[8]  W. Kutzelnigg,et al.  Wave functions with terms linear in the interelectronic coordinates to take care of the correlation cusp. III. Second‐order Mo/ller–Plesset (MP2‐R12) calculations on molecules of first row atoms , 1991 .

[9]  W. Kutzelnigg,et al.  CID and CEPA calculations with linear r12 terms , 1991 .

[10]  R. Bartlett,et al.  A study of Be2 with many‐body perturbation theory and a coupled‐cluster method including triple excitations , 1984 .

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

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

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

[14]  Werner Kutzelnigg,et al.  r12-Dependent terms in the wave function as closed sums of partial wave amplitudes for large l , 1985 .

[15]  J. G. Zabolitzky,et al.  Atomic and molecular correlation energies with explicitly correlated Gaussian geminals. III. Coupled cluster treatment for He, Be, H2, and LiH , 1984 .

[16]  J. G. Zabolitzky,et al.  Atomic and molecular correlation energies with explicitly correlated Gaussian geminals. II. Perturbation treatment through third order for He, Be, H2, and LiH , 1983 .

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

[18]  J. G. Zabolitzky,et al.  Atomic and molecular correlation energies with explicitly correlated Gaussian geminals. I. Second‐order perturbation treatment for He, Be, H2, and LiH , 1983 .

[19]  G. Diercksen,et al.  The ground state potential energy. Curve of Be2: Is the MBPT approach capable of predicting it? , 1985 .

[20]  G. A. Petersson,et al.  Complete basis set correlation energies. I. The asymptotic convergence of pair natural orbital expansions , 1981 .

[21]  G. Diercksen,et al.  A study of the reliability of different many-body methods: Potential energy curve for the ground state of Be2 , 1988 .

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

[23]  G. A. Petersson,et al.  The convergence of coupled-cluster methods for Be2 , 1991 .

[24]  Wim Klopper,et al.  Wave functions with terms linear in the interelectronic coordinates to take care of the correlation cusp. I. General theory , 1991 .

[25]  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 .