Dear Colleague,

A bug has been found in the Dissipative Particle Dynamics (DPD) code of DL_MESO
2.6.

The many-body DPD implmentation in DL_MESO, based on contributions to pairwise
forces that are proportional to the sum of localised densities for both
particles, currently only uses localised densities for their own species. While
this is adequate for single-component systems, multiple particle species barely
interact with each other and can erroneously phase separate. A further
examination of the literature suggests that localised densities based on all
species should be used instead. (Many thanks are due to Peter Vanya at the
University of Cambridge for bringing this issue to our attention.)

To fix this bug, lines 105 and 106 in field_module.f90 and lines 106 and 107 in
field_module_omp.f90 should be changed to:

    rhoi = SUM (rhomb (i, 1:nspe))
    rhoj = SUM (rhomb (j, 1:nspe))

We strongly recommend that all registered users of DL_MESO version 2.6 should
either make the above code changes or re-download the package using the
instructions received on registeration to get the corrected version of the
software, along with the recalculated SurfaceDrop test case and a slightly
modified user manual (which can also be downloaded from the DL_MESO website:
www.ccp5.ac.uk/DL_MESO). Re-registration is not required and the same password
is used for decryption.

Michael Seaton
2018-02-19