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

**From**: |
Christoph Junghans |

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

**Date**: |
Mon, 26 Nov 2012 10:33:26 -0700 |

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