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jings

金虫 (正式写手)

[交流] 【求助】MD关于平衡的问题 已有2人参与

我在建立模型的时候,用discovery动力学平衡,但是我不知道如何选取合适的dynamics time,一般现在很多人都用1ns,但是如果体系太大,选择这个时间运算会很长,我想缩短一点时间,请问有谁知道怎么从平衡图上面看出体系已经达到了平衡啊?
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linxi1454

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ghcacj(金币+2):谢谢 2010-04-02 10:26
收敛,就是某个时刻以后系统只在平均值附近涨落,涨落肯定是有的,需要根据你具体的物理量来分析,关于涨落你可以不关心,你可以这么比较
比如1ns以后系统收敛了,那么1ns-1.5ns和1.5ns到2ns之间的平均是应该近似相等的
4楼2010-04-02 10:09:25
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linxi1454

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ghcacj(金币+2):谢谢 2010-04-02 10:04
你输出系统的potential energy,如果收敛了就说明达到平衡了,你可以设置跑1ns,或者更长,隔一段时间查看一下pe是否收敛
2楼2010-04-02 10:02:59
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linxi1454

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jings(金币+5):可以加个qq么?57790934,我还不是太懂,想具体问一下你,谢谢了 2010-04-02 10:17
ghcacj(金币+4):谢谢 2010-04-02 10:26
当然,这只是一个很粗略的标记,具体可以参考如下

How to check when a system reaches it's equilibrium

This is a nontrivial question, and the answer partly depends on what you are trying to do. As David points out, if you want to do protein folding, say, your protein needs to have long enough to forget about its starting state (hence his comment about folding and unfolding). Usually that takes a prohibitively long time, though, for large proteins. So assuming you don't want to solve the protein folding problem you have to be content with something less. Definitely you want to run long enough that the protein RMSD  quits increasing, temperature and energy begin fluctuating around some relatively stable value, and so on. You can also look for things like number of protein-water hydrogen bonds if you have explicit solvent; this tends to take a much longer time to equilibrate. Probably a good suggestion is to find out what other people have done who are doing something similar to you, and make sure you equilibrate at least as much as they do.

    Just a remark about the rmsd with respect to the Xray structure: you might want to plot rmsd vs log(time), that is a better check sometimes.

    Well, rmsd is not that bad. Just that it is easier to judge a converged rmsd from a non-converged one when you plot it against log(t) instead of t. Another convergence check is the cosine content of the traj projected onto some (slow) PCA modes.

详细的可以参考这里 http://www.mdbbs.org/viewthread. ... ghlight=equilibrium
3楼2010-04-02 10:05:18
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jings

金虫 (正式写手)

麻烦具体给我一下怎么计算平均值的作法吧。我刚刚学习这个软件,还不是特别明白。谢谢哈
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5楼2010-04-02 10:27:45
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