[ESPResSo-users] Regarding Standard DPD vs Transverse DPD

[Salvador H-V]

Hi ESPResSo Users,

I am perfuming some simulations using DPD in ESPReSo to reproduce the coefficient diffusions reported in: Soft Matter 2008,4,156.

In particular i am trying to reproduce the diffusion coefficient of 4000 LJ repulsive (WCA) particles in 3D (figure1).

I create a script with the specified conditions and parameters by the authors. Then I compiled ESPResSo twice, one with DPD feature activated and another with only Trans_DPD.

Here it is the code info for each compilation:

a) Just DPD feature

ESPResSo: 3.0.2

{ Compilation status { FFTW } { MODES } { PARTIAL_PERIODIC } { ELECTROSTATICS } { MASS } { EXTERNAL_FORCES } { CONSTRAINTS } { BOND_CONSTRAINT } { EXCLUSIONS } { TABULATED } { LENNARD_JONES } { SOFT_SPHERE } { LJCOS } { LJCOS2 } { BOND_ANGLE_HARMONIC } { NPT } { DPD } }

{ Debug status { MPI_CORE FORCE_CORE } }

b) Trans_DPD 

ESPResSo: 3.0.2

{ Compilation status { FFTW } { MODES } { PARTIAL_PERIODIC } { ELECTROSTATICS } { MASS } { EXTERNAL_FORCES } { CONSTRAINTS } { BOND_CONSTRAINT } { EXCLUSIONS } { TABULATED } { LENNARD_JONES } { SOFT_SPHERE } { LJCOS } { LJCOS2 } { BOND_ANGLE_HARMONIC } { NPT } { TRANS_DPD } { DPD } }

{ Debug status { MPI_CORE FORCE_CORE } }

To run the simulations I am using for both kind of simulations (thermostats) the following commands:

thermosat off

galileiTransformParticles

set temp_ave 1.2

set gamma_dpd 1.0

set dpd_cut [ expr { ( pow ( 2.0 , 1.0/6.0 ) )*$diam } ]

thermostat dpd $temp_ave $gamma_dpd $dpd_cut WF 1

to obtain the different diffusion coefficients I have changed gamma_dpd accordingly to {0.5,1.0,2.0,3.0,5.0,7.0 & 10.0}

For the kinetic temperature and pressure I am obtaining similar values as those reported in the article for both thermostats.

Using the standard DPD thermostat I am able to obtain a similar behavior of Dt as the authors shown in figure1. However, even when I am using the same script and running the simulation with the correspondingly ESPResSo compilation I can not reproduce the results for the coefficient diffusion using the Transverse-DPD thermostat. I mean, I can not observe the drastically reduction in the coefficient diffusion as gamma_dpd increases form 0.5 to 10.

Anny comment or suggestion of possible causes of errors or mistakes in my procedure would be greatly appreciated.

Thanks a lot,

Salvador