An open-shell restricted Hartree-Fock perturbation theory based on symmetric spin orbitals

Abstract A new open-shell perturbation theory is formulated in terms of symmetric spin orbitals. Only one set of spatial orbitals is required, thereby reducing the number of independent coefficients in the perturbed wavefunctions. For second order, the computational cost is shown to be similar to a closed-shell calculation. This formalism is therefore more efficient than the recently developed RMP, ROMP or RMP-MBPT theories. The perturbation theory described herein was designed to have a close correspondence with our recently proposed coupled-cluster theory based on symmetric spin orbitals. The first-order wavefunction contains contributions from only doubly excited determinants. Equilibrium structures and vibrational frequencies determined from second-order perturbation theory are presented for OH, NH, CH, O 2 , NH 2 and CH 2 .

[1]  W. D. Allen,et al.  The analytic evaluation of energy first derivatives for two‐configuration self‐consistent‐field configuration interaction (TCSCF‐CI) wave functions. Application to ozone and ethylene , 1987 .

[2]  Peter Pulay,et al.  Generalized Mo/ller–Plesset perturbation theory: Second order results for two‐configuration, open‐shell excited singlet, and doublet wave functions , 1989 .

[3]  Curtis L. Janssen,et al.  The automated solution of second quantization equations with applications to the coupled cluster approach , 1991 .

[4]  R. Bartlett,et al.  A coupled-cluster study of inversion symmetry breaking in the F+2 molecular ion , 1991 .

[5]  Ernest R. Davidson,et al.  Perturbation theory for open shell systems , 1991 .

[6]  Dylan Jayatilaka,et al.  The form of spin orbitals for open-shell restricted Hartree—Fock reference functions , 1992 .

[7]  H. Schaefer,et al.  The analytic configuration interaction gradient method: Application to the cyclic and open isomers of the S3 molecule , 1986 .

[8]  T. H. Dunning.  Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen , 1989 .

[9]  Peter J. Knowles,et al.  Restricted Møller—Plesset theory for open-shell molecules , 1991 .

[10]  P. Jensen,et al.  The equilibrium geometry, potential function, and rotation‐vibration energies of CH2 in the X̃ 3B1 ground state , 1982 .

[11]  Björn O. Roos,et al.  Second-order perturbation theory with a complete active space self-consistent field reference function , 1992 .

[12]  Peter J. Knowles,et al.  On the convergence of the Møller-Plesset perturbation series , 1985 .

[13]  Alistair P. Rendell,et al.  A parallel vectorized implementation of triple excitations in CCSD(T): application to the binding energies of the AlH3, AlH2F, AlHF2 and AlF3 dimers , 1991 .

[14]  John F. Stanton,et al.  Many-body perturbation theory with a restricted open-shell Hartree—Fock reference , 1991 .

[15]  C. C. J. Roothaan,et al.  Self-Consistent Field Theory for Open Shells of Electronic Systems , 1960 .

[16]  L. Radom,et al.  Slow convergence of the møller-plesset perturbation series: the dissociation energy of hydrogen cyanide and the electron affinity of the cyano radical , 1987 .

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

[18]  A. D. McLean,et al.  Classification of configurations and the determination of interacting and noninteracting spaces in configuration interaction , 1973 .

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

[20]  Peter J. Knowles,et al.  Open-shell M∅ller—Plesset perturbation theory , 1991 .