Dear Colleague,

A number of bugs have been found in both the Dissipative Particle Dynamics and 
the Lattice Boltzmann Equation (LBE) codes of DL_MESO 2.6.

There is currently an incorrect condition for determining a Finitely Extensible 
Non-linear Elastic (FENE) or Worm-Like Chain (WLC) bond is within its maximum 
length: as the DPD code currently stands, this erroneous condition could cause 
division-by-zero errors. (Many thanks are due to Yaser Afshar at the University 
of Michigan, Ann Arbor, for bringing this bug to our attention and suggesting 
the following fix.)

To fix this bug, change lines 253 and 264 in bond_module.f90 and 
bond_module_omp.f90 to:

    IF (rrr<mxlen) THEN

and lines 485 and 983 in bond_module.f90 (lines 519 and 1011 in 
bond_module_omp.f90) to:

    IF (rrr>=mxlen) THEN

When applying the Lishchuk continuum-based model with non-periodic boundary 
conditions in serial calculations (i.e. without MPI), a bug currently exists 
when the second-order gradient stencil is used that can cause fluid drops to 
disappear. (Many thanks are due to Kallum Burgin and Meredith Ellis, both at 
Sheffield Hallam University, for bringing this bug to our attention and 
suggesting a fix.)

To correct this bug, change lines 1011 to 1013 in lbpFORCE.cpp to:

    spos2 = (fCppMod(xpos+2*lbvx[m], lbdm.xouter)  * lbdm.youter +
             fCppMod(ypos+2*lbvy[m], lbdm.youter)) * lbdm.zouter +
             fCppMod(zpos+2*lbvz[m], lbdm.zouter);

noting that the variable name should change from spos1 to spos2. 

Further changes are suggested for the fsCalcPhaseIndex_Lishchuk subroutine to 
improve computational performance. These involve changing the definitions of 
spos and spos1 in lines 758 to 760, lines 769 to 771 and lines 784 to 786 in 
lbpFORCE.cpp to, e.g.

    spos = ((i+lbvx[m]) * Ymax + j+lbvy[m]) * Zmax + k+lbvz[m];

which remove the superfluous need to use the fCppMod function.

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 registration to get the corrected version of the 
software. Re-registration is not required as the decryption password has not 
changed.

Michael Seaton
2017-08-10