Re: [ESPResSo-users] parameters about conservative force in DPD method

[Christoph Junghans]

2012/11/26 guozhicheng222 <address@hidden>:
> Dear all
>
>        I don not understand the number of parameters in the DPD interaction
> used in ESPresSo simulation. The command form described as follow:
>
> inter type1 type2 inter_dpd gamma r_cut [WF wf tgamma tr_cut TWF twf]
>
> Obviously, there is just one parameter of gamma to depict the dissipative
> force and random effect derived from the fluctuation-dissipation relation
> (σ2=2γkBT, σ and γ denote the strength of noise and friction, respectively).
I think you go a bit misled. DPD has the freedom to choose one
function as the fluctuation-dissipation relation includes w_D(r).
And then it is commontly chosen that w_D(r)=gamma w^hat_D(r), where
w^hat_D(r) is a normalized function with a cutoff (the r_cut
parameter) and a shape (the wf parameter).
Note that, in espresso, only a theta and 1/r function are implemented.
> However, the force acting on a particle has three parts, each of which is a
> sum of pair forces. The three contributions are a conservative force FijC, a
> dissipative force FijD and a random force FijR. Therefore, I want know how
> to describe the conservative term (FijC) in ESPresSo simulation.
The conservative part of DPD is called hat interaction (define HAT) in espresso.

Christoph

> Moreover,
> what is the way of analyzing the chemical bond broken in ESPresSo based on
> DPD method. I am sincerely waiting for your response. Thanks!
>
>
>
> Best wishes!
>
>
>
> Zhicheng Guo
>
>
>



--
Christoph Junghans
Web: http://www.compphys.de