********>bugfix.47:
Author: Jason Swails
Date: 8/31/2009

Programs: sander

Description: Constant pH with closely interacting residues can misbehave
due to an incorrectly formed tpair array.  Further problems occur in
parallel simulations since the tpair array is only updated on the master
node in runmd.f

Apply the following patch to $AMBERHOME/src/sander/constantph.f
                             $AMBERHOME/src/sander/runmd.f

------------------------------------------------------------------------------
--- constantph.f     	2009-08-31 19:23:15.000000000 -0400
+++ constantph.f	2009-08-31 19:25:23.000000000 -0400
@@ -52,7 +52,7 @@
    integer :: i, j, pi,  ti, tj
    _REAL_ :: xij, yij, zij
 
-   pi = trescnt                 !Start dynamic list after header
+   pi = trescnt + 1             !Start dynamic list after header
 
    do i = 0, trescnt - 1
       tpair(i) = pi             !Start index into list for current residue


--- runmd.f    	2009-08-31 19:15:05.000000000 -0400
+++ runmd.f	2009-08-31 19:32:57.000000000 -0400
@@ -798,10 +798,15 @@
    end if
 
    ! Constant pH setup
-   if ((icnstph /= 0) .and. (mod(irespa,ntcnstph) == 0)) then
-      call cnstphbeginstep(ix(icpstinf),ix(icpresst), &
-            ix(icptrsct), &
-            xx(lcpene),xx(lcpcrg),xx(l190),icpselres,icpselstat, cnstph_rand_gen,ix(icptpair))
+   if (icnstph /= 0) then
+      if (ntnb.eq.1) then
+         call cnstphupdatepairs(x,ix(icptrsct),ix(icphidx),ix(icptpair))
+      end if
+      if (mod(irespa,ntcnstph) == 0) then
+         call cnstphbeginstep(ix(icpstinf),ix(icpresst), &
+               ix(icptrsct), &
+               xx(lcpene),xx(lcpcrg),xx(l190),icpselres,icpselstat, cnstph_rand_gen,ix(icptpair))
+      end if
    end if
 
    !--------------------------------------------------------------
@@ -2053,7 +2058,6 @@
          if (icnstph /= 0) then
             call cnstphwriterestart(ix(icpstinf),ix(icpresst),ix(icpptcnt), &
                   ix(icptrsct), xx(lcpene),xx(lcpcrg))
-            call cnstphupdatepairs(x,ix(icptrsct),ix(icphidx),ix(icptpair))
          end if
 
       end if  ! (ixdump)
------------------------------------------------------------------------------
Temporary workarounds: None