Dear Colleague,

A bug in the parallel version of the Dissipative Particle Dynamics code has been 
discovered.

The deport routine in domain_module.f90 contains calls to the subroutines 
contract_bndtbl, contract_angtbl and contract_dhdtbl (in lines 214-216) which 
are supposedly conditional on finding any bonds that need to be transferred from 
the current processor to its neighbour. The conditions specified in lines 214, 
215 and 216 do not, however, guarantee that these subroutines are called when 
they need to be and thus outdated bond data might therefore be retained in the 
tables, leading to an error message stating a bond cannot be found and 
terminating DL_MESO_DPD.

It should be noted that this bug does not affect the accuracy of calculations, 
merely the ability to carry them out. It is also not applicable for the serial 
version of the DPD code. (Many thanks are due to Luo Zhonglin for drawing 
attention to this bug.)

The bug can be fixed by changing line 72 of domain_module.f90 to:

      LOGICAL :: safe, bondmove

adding the following immediately after line 87:

      bondmove = .false.

modifying the IF statements in lines 137-142, 156-162 and 176-183 by including 
bondmove = .true. in each group of commands, e.g. lines 156-162 should be 
changed to:

      IF (lb==angtbl (j, 2)) THEN
        iang = iang + 1
        bufout (imove + 10 + 2 * ibond + 3 * iang) = DBLE (angtbl (j, 1))
        bufout (imove + 11 + 2 * ibond + 3 * iang) = DBLE (angtbl (j, 3))
        bufout (imove + 12 + 2 * ibond + 3 * iang) = DBLE (angtbl (j, 4))
        angtbl (j, 4) = -1
        bondmove = .true.
      END IF

and changing lines 214-216 to:

      IF (bondmove) THEN
        CALL contract_bndtbl
        CALL contract_angtbl
        CALL contract_dhdtbl
      END IF

The above changes will ensure that the subroutines to remove old bond data will 
be called whenever any bond/angle/dihedral needs to be moved.

This bug fix has been applied to the current DL_MESO release and a corrected 
version may be downloaded by registered users of 2.3 without re-registering and 
decrypted using the same password.

Michael Seaton
2011-03-11