********> bugfix.62
Correction Author: Yax Sun and David A. Pearlman
Correction Date: 03/30/94

Programs: GIBBS

Severity: Moderate

Problem: 

       The number of degrees of freedom calculated for a system
       with all the following conditions would be 3 too large:

       1) center of mass motion being removed (NTCM=1 or NSCM>0)
       2) no periodic boundaries used (NTB=0)
       3) (If NTT=2 or NTT=5) ISOLVP = 0.

Affects: 

       The effective temperature of the system would be off. 
       The percentage by which the temperature would be off is
       given by approximately 3/actual-number-of-degrees-of-freedom.
       For all but the smallest systems, this will probably be 
       insignificant.

Cause: 

       In effecting a previous bugfix to handle degrees of freedom for
       the special case of one atom solute systems, a construct 
       was inadvertently introduced which would force this case to be
       applied to many systems.

Fix:  Make the following changes to routine MDREAD in Gibbs

---Gibbs: To routine MDREAD in file giba.f -----------------------------

*** OLD giba.f
--- NEW giba.f
***************
*** 1158,1187 ****
        END IF
  C
  c ------------------------------------
- c set/reset dependent vars
- c ------------------------------------
- c
-       nsolut = 1
-       if (ntt.eq.2 .or. ntt.eq.5) then
-         if (nspstr.gt.0) nsolut = nspstr
-         if (isolvp.gt.0) nsolut = isolvp
-       endif
-       if ((ntcm.eq.1 .or. nscm.gt.0) .and. ntb.eq.0) then
-         ndfmin = 6
-         if (nsolut.eq.1) ndfmin = 3
-         if (nsolut.eq.2) ndfmin = 5
-       else
-         ndfmin = 0
-       endif
-       if(ibelly .eq. 1) then
- c          --- No COM Motion Removal, ever. ---
-            ntcm = 0
-            nscm = 9999999
-            ndfmin = 0
-       endif
- 
- C
- c ------------------------------------
  c check range on input vars
  c ------------------------------------
  c
--- 1158,1163 ----
***************
*** 1252,1261 ****
          write(6,'(/2x,a,i3,a)') 'NTCM (',ntcm,') must be 0 or 1.'
          inerr = 1
        endif
-       if (nsolut.eq.0 .and. ndfmin.ne.0) then
-         write(6,'(/2x,a)') 'NTCM or NSCM set but no solute atoms'
-         inerr = 1
-       endif
        if (isvat.lt.0 .or. isvat.gt.3) then
          write(6,'(/2x,a,i3,a)') 'ISVAT (',isvat,') must be in 0..3.'
          inerr = 1
--- 1228,1233 ----
***************
*** 1426,1431 ****
--- 1398,1430 ----
        NSM = 0
        NRAM = 0
  C
+ c ------------------------------------
+ c set/reset dependent vars
+ c ------------------------------------
+ c
+       nsolut = nrp
+       if (ntt.eq.2 .or. ntt.eq.5) then
+         if (nspstr.gt.0) nsolut = nspstr
+         if (isolvp.gt.0) nsolut = isolvp
+       endif
+       if ((ntcm.eq.1 .or. nscm.gt.0) .and. ntb.eq.0) then
+         ndfmin = 6
+         if (nsolut.eq.1) ndfmin = 3
+         if (nsolut.eq.2) ndfmin = 5
+       else
+         ndfmin = 0
+       endif
+       if(ibelly .eq. 1) then
+ c          --- No COM Motion Removal, ever. ---
+            ntcm = 0
+            nscm = 9999999
+            ndfmin = 0
+       endif
+       if (nsolut.eq.0 .and. ndfmin.ne.0) then
+         write(6,'(/2x,a)') 'NTCM or NSCM set but no solute atoms'
+         call mexit(6,1)
+       endif
+ C
  C Hardwire some variables that refer to stupid or incorrectly implemented
  C options:
  C
------------------------------------------------------------------------------


Temporary workarounds: 

     None.

Routines affected:

     GIBBS   Routine MDREAD in file ...amber4/src/gibbs/mdread.f        

--