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)