NAME

       stable - MO Hessian stability analysis program

DESCRIPTION

       The program stable performs a stability analysis on the molecular orbitals by diagonalizing the molecular
       orbital Hessian.  The analysis includes orbital rotations which may break spin or spatial  symmetry.   If
       an  instability  is  detected  (i.e.,  there  are  negative  eigenvalues of the MO Hessian), the previous
       Hartree-Fock self consistent field (SCF) computation has landed  on  a  local  minimum,  not  the  global
       minimum,  in orbital rotation space.  For spatial- or symmetry-breaking rotations, this merely means that
       there is another orbital occupation or a UHF wavefunction with a lower energy.   For  instabilties  which
       preserve  the  reference  type  (RHF  or  UHF)  and  are  totally  symmetric,  this suggests that the SCF
       computation has simply found the wrong solution and should be re-run using a new initial guess.

       Instabilities corresponding to spatial symmetry breaking rotatios  can  be  resolved  by  re-running  the
       calculation  in  a  lower  computational  point group.  (It may also be necessary to employ some trick to
       break the symmetry of the initial guess wavefunction).   Instabilities  corresponding  to  spin  symmetry
       breaking rotations (RHF->UHF) can be resolved by re-running the SCF using a UHF reference.

       For  UHF  wavefunctions  with  totally-symmetric  instabilities, it is possible to follow the instability
       automatically toward the global minimum by setting FOLLOW=TRUE.

INPUT FORMAT

       Input for this program is read from the file The following keywords are valid:

       CACHELEV = integer
              This is the cache level used for the DPD files.  It functions the same  way  as  in  the  coupled-
              cluster codes.  Currently, this is hardwired to 0.

       FOLLOW = boolean
              If TRUE, then the eigenvector corresponding to the most negative eigenvalue of the MO Hessian will
              be followed to try to find a lower energy Hartree-Fock solution.  The orbitals  will  be  rotated,
              and the cscf module should be re-run using these new guess orbitals.

       NUM_EVECS_PRINT = integer
              Gives the number of MO Hessian eigenvectors to print.

       PRINT = integer
              The print level determines how much information is printed by the program.  Values typically range
              from 1 (minimal printing) to 5 (very verbose printing for debugging only).  The default is 1.

       REFERENCE = string
              This is the reference type, RHF, ROHF, or UHF.  The default is RHF.

       SCALE = real
              This is the scale factor used for taking steps in eigenvector following.  Normal values  would  be
              between 0 and 1.  The default is 0.5.

                                                   23 Aug, 2003                                        stable(1)