|From:||Axel Kohlmeyer <akohlmey@...24...>|
|Date:||Fri, 18 Aug 2017 09:56:54 -0400|
Dear Axel,thanks a lot for the clarification. So I understand that the input below fully describes the DPD in LAMMPS:pair_style dpd T rc seedpair_coeff * * a gamma rcfix 1 all nveI am not sure if I am the only one, but I think if would be very useful if these lines were stated in the DPD section of the manual.
To improve my understanding I am now trying to reproduce a more complex system -- phase separation of a symmetric diblock copolymer, as described in this paper. Polymerisation N = 10, like bead interaction 25 and cross interaction 50. In theory I should be easily getting a lamellar phase after as few as 20k steps, but in practice I am see only a disordered phase. However, I was able to get this phase with the DL_MESO package. I am sending the screenshots and input file attached.Can you please suggest what I am doing wrong? I have tried everything I could think of.
Thank you in advance.Kind regards,On 17 August 2017 at 18:07, Axel Kohlmeyer <akohlmey@...24...> wrote:On Thu, Aug 17, 2017 at 12:16 PM, Peter Vanya <pv278@...690...> wrote:Dear all,I have spent a considerable amount of time trying to make DPD with the thermostat work correctly, yet my results are clearly wrong. Can you please help?Reading the manual, I understand that there are in general two options for thermostatting, starting from temperature T, the cutoff, interaction parameter a, friction gamma, and the seed:1.pair_style dpd T cutoff seedpair_coeff * * a gammafix 1 all nvefix 2 all langevin T T gamma seed2.pair_style hybrid/overlay dpd T cutoff seed dpd/tstat T T cutoff seedpair_coeff * * dpd a gammapair_coeff * * dpd/tstat gammafix 1 all nveboth of these inputs make no sense.the effect of pair style dpd/tstat is *already included* in pair style dpd. so there is no point in using hybrid/overlay. the reason for dpd/tstat is to apply it to other potentials.similarly, it is not correct to use fix langevin in combination with pair style dpd. you are applying a thermostat twice with conflicting approaches. that is likely to be bogus.axel.As far as I understand, the first option makes the particles interact with an implicit solvent and not each other and so is not a proper DPD. Hence, only the second option remains.Trying the second option on a pure DPD liquid, the temperature goes up to 3.5 and does not settle (it should settle at 1.0), and the RDF is totally incorrect close to r = 0.Can I please ask what exactly wrong with my input, and how to get it right? I tried to follow the manual as closely as it gets. Attached I am sending the data and input file together with the RDF.Thank you in advance.Kind regards,
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