stable(1)																 stable(1)

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 mini-
       mum, 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 cor-
       responding 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  mini-
       mum 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)