NAME

       dboc - Diagonal Born-Oppenheimer Correction using HF and CI wave functions.

DESCRIPTION

       The program dboc computes Diagonal Born-Oppenheimer Correction (DBOC) using HF and CI wave functions.

REFERENCES

       "Cartesian" DBOC formula (aka Born-Handy-Pulay formula):

       1.     N. C. Handy, J. Yamaguchi, and H. F. Schaefer, J. Chem. Phys. 84, 4481 (1986).

       Justification for the "Cartesian" DBOC formula:

       1.     W. Kutzelnigg, Mol. Phys. 90, 909 (1997).

       Finite-difference formulation of DBOC at CI level

       1.     E. F. Valeev and C. D. Sherrill, J. Chem. Phys. 118, 3921 (2003).

INPUT FORMAT

       The following keywords are valid:

       WFN = string
              Specifies  the  type  of  wave function desired. The only valid entries at the present are SCF and
              DETCI. There is no default.

       REFERENCE = string
              Specifies the type of orbitals used for the single-determinant reference function.  Valid  choices
              are RHF, ROHF, and UHF.  There is no default.

       PRINT = integer
              Determines the verbosity of the output.  A value of 0 (the default) specifies minimal printing.

       :DBOC:DISPLACEMENT = real
              Determines the finite difference step (in a.u.). The default is 0.0005 a.u.

       :DBOC:DISP_PER_COORD = integer
              Determines  the  number  of  displacements  for  each coordinate. Set it to 2 to compute DBOC with
              standard accuracy (enough significant digits for up to second derivatives; DBOC accurate to square
              of displacement size), and 4 to compute DBOC with improved accuracy (DBOC accurate to  the  fourth
              power of displacement size).  The default is 2.

       ISOTOPES = string_vector
              Specifies  which  isotope  to  use  for  each atom. Each string should specify an isotope label as
              defined in include/masses.h. By default, most abundant isotopes are used for each element.

       :DBOC:COORDS = vector
              This keyword should only be used by advanced users who are familiar with how DBOC is evaluated  by
              finite  differences.   The keyword may be used to specify the cartesian nuclear coordinates to use
              in the sum expression for DBOC, their respective coefficients, and whether they are  symmetric  or
              nonsymmetric  with  respect  displacements.   dboc can use symmetry to minimize the number of wave
              function computations.  Hence this keyword need only be  used  for  diagnostic  purposes  or  when
              displacements  along  different  coordinates  need  to  be run separately (e.g.  require different
              occupation vectors).  The value for this keyword is an array  of  3  element  vectors.  The  first
              element of each vector is the index of the cartesian coordinate which to include into the sum. The
              second  element  is  a  real coefficient for the respective term in the DBOC expression. The third
              element is a string that can take two values, symm and nonsymm, which indicate that the coordinate
              is symmetric or nonsymmetric with respect to displacements, respectively.   Indices  are  C-style,
              i.e. from 0 to 3*natom-1.

                                                 30 August, 2003                                         dboc(1)