Dear Colleague, A bug has been discovered in the Dissipative Particle Dynamics code. The short-range electrostatic force expression for the Ewald sum with Slater- type smearing is currently incorrect, both in the code itself and as stated in the user manual (equation 10.54). In the first bracketed term, the fraction with the square root of pi should also have the product of the Ewald convergence parameter and the interparticle distance. (Many thanks are due to Martin Lisal for bringing this error to our attention.) To fix this bug, please change lines 133 and 134 in ewald_module.f90 to the following: eforce = 0.25d0 * gammaelec / pi * qiqj * (2.d0 * alphaew * rrr / rtpi * & &EXP (-alphaew * alphaew * rsq) + erfr) * ((1.d0 - scrn) * & &(1.d0 + 2.d0 * betaew * rrr * (1.d0 + betaew * rrr))) / (rsq * rrr) A corrected user manual with the correct expression for the electrostatic force can now be downloaded from the DL_MESO website at www.ccp5.ac.uk/DL_MESO In the same module, a significant increase in computational efficiency for calculating the same force can be achieved by changing line 60 to: IF (safe .AND. ccc (ltp (i))/=0.d0) THEN and line 123 to: IF (rsq1.d-16) THEN These changes ensure that only charged particles are included in the cell lists for short-range Ewald forces, which can vastly reduce the number of particle pairs that need to be searched. An error in the CONTROL-neutral file for the Polyelectrolyte case study has also been discovered. The line describing the polymer species (POLY) currently applies a charge of +0.5 on each bead: this should be changed to 0.0 to give a neutral polymer, i.e. line 33 in the CONTROL-neutral file should be changed to SPEC POLY 0 1.0 78.3 1.0 0.0 We strongly recommend that all registered users should either make the code changes shown above or download DL_MESO again using the instructions they received on registration to obtain the corrected version of the software. Re- registration is not required and the same password is used for decryption. Michael Seaton 2011-08-09