********>Bugfix 6:
Author: Ross Walker
Date: 06/02/2008

Programs: sander

Description: There is a small possibility that QMMM calculations run
             in parallel where the diagonalization routine is set to
             automatically select the fastest routine can either hang
             due to an MPI race condition or quit with an MPI message
             synchronization error. This problem only occurs if the 
             automatic diagonalization selection routine finds that
             pseudo diagonalization should be turned off for performance
             reasons.  This occurs because all threads were not being
             informed of the pseudo diagonalization change.

Fix: apply the following patch to src/sander/qm2_load_params_and_allocate.f
                              and src/sander/qmmm_module.f

------------------------------------------------------------------------------
--- qmmm_module.f	2008-06-02 17:07:57.000000000 -0700
+++ qmmm_module.f	2008-06-02 17:10:58.000000000 -0700
@@ -888,7 +888,7 @@
                   stat=ier)
        REQUIRE(ier == 0)
      end if
-     if (qmmm_nml%diag_routine==7 .and. (.not. qmmm_nml%allow_pseudo_diag)) then
+     if (qmmm_mpi%commqmmm_master .and. qmmm_nml%diag_routine==7 .and. (.not. qmmm_nml%allow_pseudo_diag)) then
        !we allocated pdiag_scr_norbs_norbs to store the unpacked matrix so make sure
        !we deallocate it.
        deallocate(qmmm_scratch%pdiag_scr_norbs_norbs, stat=ier)
--- qm2_load_params_and_allocate.f	2008-06-02 16:36:55.000000000 -0700
+++ qm2_load_params_and_allocate.f	2008-06-02 17:07:42.000000000 -0700
@@ -1491,6 +1491,8 @@
 !broadcast the final chosen routine. Not strictly necessary at present but may help with
 !debugging later on.
           call mpi_bcast(qmmm_nml%diag_routine,1,MPI_INTEGER,0,qmmm_mpi%commqmmm,ier)
+!Note we also need to broadcast the value of allow_pseudo_diag in case it changed.
+          call mpi_bcast(qmmm_nml%allow_pseudo_diag, 1, mpi_logical, 0, qmmm_mpi%commqmmm, ier) 
 #endif
         else
           if (qmmm_mpi%commqmmm_master) &
------------------------------------------------------------------------------

Temporary workarounds: Manually turn off pseudo diagonalizations in your input
                       file.