********>Bugfix 42:
Author: Ross Walker
Date: 04/15/08

Programs: sander

Description: QM/MM Calculations with semiempirical should be restricted
             to singlets only due to the lack of support for calculating
             the spin pairing energy vs unoccupied orbital energy for
             unpaired electrons.
             
Fix:  apply the following patch to amber9/src/sander/qmmm_module.f
      apply the following patch to amber9/test/makefile

----------------------------------------------------------------------------
--- src/sander/qmmm_module.f	2008-04-15 10:05:39.000000000 -0700
+++ src/sander/qmmm_module.f	2008-04-15 10:06:23.000000000 -0700
@@ -100,7 +100,7 @@
  integer :: qmtheory  !Level of theory to use for QM region (Hamiltonian) 1 = PM3, 2 = AM1, 3 = MNDO (Default = PM3)
                       !                                                   4 = PDDG/PM3, 5 = PDDG/MNDO, 6 = PM3CARB1
  integer :: qmcharge  !Charge of the QM region in electron units - must be an integer charge. (Default = 0)
- integer :: spin      !Spin state - default = 1 (singlet). Valid values = 1 to 6.
+ integer :: spin      !Spin state - default = 1 (singlet). Current Valid values = 1 (alternate options not currently available).
  integer :: verbosity !Controls amount of info printed about qm part of calc - (Default = 0)
  integer :: itrmax    !Maximum number of SCF cycles to conduct before assuming convergence has failed. (Default = 1000).
  integer :: qmshake   !Whether to shake qm atoms if ntc>1 (default = 1 - shake QM atoms) 0 = do not shake.
@@ -1297,7 +1297,9 @@
    call int_legal_range('QMMM: (Density Matrix Convergence) ', tight_p_conv,0,1)
    call float_legal_range('QMMM: (SCF Convergence) ', scfconv,1.0D-16,1.0D0)
    call int_legal_range('QMMM: (PRINT CHARGES) ', printcharges,0,1)
-   call int_legal_range('QMMM: (Spin State) ', spin,1,6)
+   call int_legal_range('QMMM: (Spin State) ', spin,1,1)
+!RCW: Currently limit spin state to singlets only since the code for spin>1 does not exist / work at present.
+!     WARNING - IF WE LATER ALLOW SPIN>1 qm2_densit will need updating.
    call int_legal_range('QMMM: (Peptide Correction) ',peptide_corr,0,1)
    call int_legal_range('QMMM: (QM-QM RIJ in Core) ',qmqmrij_incore,0,1)
    call int_legal_range('QMMM: (QM-MM RIJ in Core) ',qmmmrij_incore,0,1)

--- test/Makefile	2008-04-15 10:09:57.000000000 -0700
+++ test/Makefile	2008-04-15 10:01:53.000000000 -0700
@@ -128,11 +128,6 @@
 	cd qmmm2/pure_QM_MD; ./Run.nma_md_qmgb1
 	cd qmmm2/pure_QM_MD; ./Run.nma_md_qmgb2
 	cd qmmm2/pure_QM_MD; ./Run.nma_md_qmgb2_saltcon
-	cd qmmm2/pure_QM_MD; ./Run.nma_md_doublet
-	cd qmmm2/pure_QM_MD; ./Run.nma_md_triplet
-	cd qmmm2/pure_QM_MD; ./Run.nma_md_quartet
-	cd qmmm2/pure_QM_MD; ./Run.nma_md_quintet
-	cd qmmm2/pure_QM_MD; ./Run.nma_md_sextet
 	cd qmmm2/pure_QM_MD; ./Run.C6H4FCL_md
 	cd qmmm2/pure_QM_MD_shake; ./Run.nma_md
 	cd qmmm2/pure_QM_MD_tight_p; ./Run.nma

------------------------------------------------------------------------------
Temporary Workarounds: Do not use spin>1 in qmmm namelist.