Dear Colleague,

A couple of bugs have been found in the Dissipative Particle Dynamics (DPD) 
code of DL_MESO 2.6.

When applying linear shear using Lees-Edwards boundary conditions using a small 
number of processors, it is possible for the DPD code to hang if the boundaries 
are separated by a single processor. This is due to repeated use of the same 
MPI communicators to move particles in opposite directions from each processor. 
To avoid this conflict, changes to the shear-based communication subroutines in 
domain_module.f90 and the routines that call them are required to allow second 
calls to the former routines to use different MPI communicators.

If charges are applied to a linearly-shearing system using Ewald sums, the code 
may currently stop partway through a simulation with error messages related to 
truncated MPI communications. This is due to unexpected changes in the 
variables holding the distance by which the periodic box is shifted when 
communications are applied: as the nature of these changes can vary from 
processor to processor, the required adjustments to reciprocal vectors due to 
shear may also vary among the processors and result in different numbers of 
vectors within range for the given reciprocal vector sizes. Further changes 
to the shear-based communication subroutines in domain_module.f90 are required 
to prevent these distances from being modified. (Many thanks are due to 
Breanndán Ó Conchúir at IBM Research for bringing this bug to our attention.)

Since the required code changes are substantial, they will not be outlined in 
this email. We therefore strongly recommend that all registered users of 
DL_MESO version 2.6 should re-download the code using the instructions they 
received at registration to obtain the corrected version of the software. The 
decryption password has not changed and thus re-registration is not required. 
Small changes have also been made to the user manual, a revised version of 
which can be obtained either with the corrected DL_MESO package or from the 
DL_MESO website (www.ccp5.ac.uk/DL_MESO).

Michael Seaton
2018-03-28