Dear Yun-Peng, I now can achive my goal using Nose method even when I set the temperature to 0K. But when I set temperature to 0K, a question will rise that is if I set the MD.NoseMass to 1.0 Ry*fs**2 I can not get the results I want, while set it to 10.0 Ry*fs**2 or higher, I can get the results.
I read the manual and the paper you suggest me and also 'Progress of Theoretical Physics Supplement No. 103, 1991' which Andrei Postnikov ever suggested someone to read. And I found this parameter can scale the time of the dynamics. That is when it is 10, and if the step I set is 1fs, in the simulation, the time step is 1/10=0.1 fs. Am I right? Also, this parameter describes the coupling of the external thermal bath to the physical system. This parameter has a dimension of moment of inertia. I can not understand your meaning by "If NoseMass is infinitely large, its movement can not be changed and this is NVE ensemble in fact." Is this parameter describe the moment of inertia of the physical system or the external thermal bath? It seems the physical system. The larger this parameter, the harder to change the physcial system, and the samller coupling between the physcial system and the bath. However, if this holds, why the simulation time step is shortened by it? (I think the bigger coupling ,the easier to change the physcial system, then wen can shortened the time step in the simulation.) I have no idea, how to set this parameter reasonably. Please help me out this quesiton. Best Guangping 2011-10-05 Guangping Zhang 发件人: "Guangping Zhang" <[email protected]> 发送时间: 2011-10-02 19:21 主 题: Re: Re: Re: [SIESTA-L] MD simulation in SIESTA 收件人: "siesta-l" <[email protected]> Dear Bartek and Yun-Peng, First thanks for your suggestions. I want to investigate the decomposation of a molecule which adsorbes on the metal surface. I remeber someone did a simulation a H2 molecule on Cu surface (I can not remeber it clearly) using molecular dynamics. So I want to follow this idea to investigate my system. I indeed use the method of Anneal to simulate the process. I could see the decomposation. At the beginning of the simulation, the decomposation takes place. I doubt this is the effect of temperature, becasue if I use 300K as the inintal temperature I can not see this process. Yun-Peng suggest me to do a constant temperature simualtion, and the temperature is under going. I wonder if I use a constant temperature simulation, I can not see this process. Thanks for your instructions. Best wishes Guangping 2011-10-02 Guangping Zhang 发件人: Bartek Szyja <[email protected]> 发送时间: 2011-10-02 18:14 主 题: Re: Re: [SIESTA-L] MD simulation in SIESTA 收件人: "[email protected]" <[email protected]> On Sun, 2011-10-02 at 11:01 +0200, Guangping Zhang wrote: > I say non-local minimum to mean that the minimum is not the local > minimum that near the initial configuration. I want the system to go > over some barriers and find a lower minimum. I don't think MD is a good choice in this case. There is metadynamics but as far as I know there is no implementation of it in SIESTA. Some variant of Monte Carlo could also be a good option. If you insist on SIESTA, you can try to set initial temperature relatively high, so the system is able to overcome the barriers, and cool it down during the run, so it settles in a "hopefully" more stable minimum - but you'll never be sure it really is the one you want. I guess the most reasonable approach is the one suggested by Yun-Peng - try different starting configurations and see what happens to your system. Good luck, Bartek
