The following are the changes I made to main.f to account for rigid atoms.

Addtions:       

 44        dimension iswitch(MAXATM) 

    53        call GetInpV(NDIM,MAXATM,MAXTYP,natom,h0,kcell,Omega,rnuc,
    54       &   zchg,vnuc,amass,nttot,ia,nnuc,hard,chi,zeff,zeta,potparm,time,
    55       &   iswitch) 

  4995        subroutine GetInpV(NDIM,MAXATM,MAXTYP,natom,ucell,kcell,Omega,
  4996       & rnuc,zchg,vnuc,amass,nttot,ntype,nnuc,hard,chi,zeff,zeta,
  4997       & potparm,time,iswitch)

  5027        dimension iswitch(MAXATM)  

  5049            call RdInpV(NDIM,MAXATM,MAXTYP,natom,ucell,kcell,Omega,rnuc,
  5050       &      zchg,vnuc,amass,nttot,ntype,nnuc,hard,chi,zeff,zeta,potparm,
  5051       &      iswitch)

 5160        subroutine RdInpV(NDIM,MAXATM,MAXTYP,natom,ucell,kcell,Omega,rnuc,
  5161       &   zchg,vnuc,amass,nttot,ntype,nnuc,hard,chi,zeff,zeta,potparm,
  5162       &   iswitch)

  5193        dimension iswitch(MAXATM)    

 5241               call GtReal(nn,nline,line,iswitch(natom))  

 5247               iswitch(natom)=0 


After all these additions, it seems to compile.  Now for more...

    98        do i=1,natom
    99           if (iswitch(i).eq.2) then
   100              force(1,i)=0.0
   101              force(2,i)=0.0
   102              force(3,i)=0.0
   103           endif
   104        enddo


   266            do j=1,natom
   267               if (iswitch(j).eq.2) then
   268                  force(1,j)=0.0
   269                  force(2,j)=0.0
   270                  force(3,j)=0.0
   271               endif
   272            enddo