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doudouding木虫 (小有名气)
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[交流]
【求助】castep中怎样设置温度
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想计算体系在不同温度下的弹性常数，没找到在哪里能设置温度，请高手指点 [ Last edited by freshgirl on 2009-6-25 at 15:36 ] |
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fegg7502(金币+3,VIP+0):thank you very much!
fegg7502(金币+3,VIP+0):thank you very much!
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4L 的结论我总是听到 不知道是不是真的 ？ Thermodynamic calculations In principle, if the molecular geometry, energy, and vibrational frequencies are known, the thermodynamics properties (enthalpy, entropy, free energy) of the molecule can be calculated (Stull and Prophet, 1971). The results can be displayed using the Thermodynamic properties dialog, or viewed in the VAMP output file. There is, however, a fundamental inconsistency inherent in the parameterization of semiempirical methods to reproduce heats of formation. The energy calculated by VAMP is the internal energy of a hypothetical motionless (Born-Oppenheimer) state. To relate this energy to heats of formation at 298 K, an atom-based scheme is used, assuming that the energy difference between the Born-Oppenheimer state and the molecule at 298 K can be treated in an additive fashion. This means that the zero-point energy and the energy required to warm the molecule to 298 K are assumed to be identical for isomers. This is clearly not the case and can lead to errors of up to 5 kcal mol-1. A further problem arises in the calculation of the thermodynamic properties. As the methods are parameterized to reproduce the heat of formation at 298 K, this temperature must be used as the reference point for thermodynamics calculations. The calculation, however, gives an energy for a motionless molecule. This leads to a basic inconsistency. Thermodynamics calculations yield entropy, enthalpy, and free energy changes between the Born-Oppenheimer state and the temperature in question. The heat of formation scale must, however, be adjusted so that the value at 298 K is the same as that given in the normal calculation. The result is that, in effect, we have to work with a fictitious Born-Oppenheimer energy in thermodynamics calculations. The best procedure is simply to ignore the "heat of formation" and to calculate thermodynamic quantities for reactions based on the Born-Oppenheimer energy and the calculated entropy and enthalpy changes, as for ab initio calculations. Using the thermodynamic data Once the enthalpy, entropy, and free energy of the molecule are calculated as a function of temperature, the results can be used to compute the heat of formation at any temperature. The heat of formation at 298 K is written to the VAMP output file and can be adjusted for different temperatures as follows: Display the results using the Thermodynamic properties dialog or view them in the VAMP output file. For the temperature of interest, say 100 K, compute the temperature-dependent contribution, enthalpy minus temperature times entropy (E - TS). Compute E - TS at 298 K. If you did not compute the thermodynamics at exactly 298 K, pick the temperature closest to it (e.g., 300 K) or estimate it by interpolation. Compute the difference in E - TS at the two temperatures and adjust the heat of formation at 298 K by that amount. For example, say that E - TS at 100 K is 0.5 kcal mol-1 and the value at 298 K is 2.2 kcal mol-1. You would compute the heat of formation at 100 K by subtracting 1.7 kcal mol-1 (2.2 - 0.5) from the heat of formation at 298 K given in the VAMP output file. Further information |
6楼2009-01-07 09:32:38
哪里能设置温度?
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fegg7502(金币+2,VIP+0):thank you very much!
fegg7502(金币+2,VIP+0):thank you very much!
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请问大家，有谁在castep模块，改变温度进行计算的，怎么改变温度呢？ Supercondcor(274056850) 21:17:48 castep不能改变温度进行计算 桔迷(183331864) 21:19:11 当然可以 castep 和 dmol的分子动力学 桔迷(183331864) 21:19:41 不过做好死机的准备 计算量相当大 sixhair (30473721) 21:20:12 就看你服务器强不强 不过不一定要计算玩的 桔迷(183331864) 21:21:01 嗯 娃娃(35861885) 21:21:27 那怎么设置啊，请教一下 桔迷(183331864) 21:23:31 不知道 你看看ｃａｓｔｅｐ 的ｓｅｔｕｐ选项中有个ｄｙｎａｍｉｃｓ 桔迷(183331864) 21:23:49 算恒定温度用NVT系综 娃娃(35861885) 21:26:09 sixhair ：知道怎么改变温度吗 娃娃(35861885) 21:26:38 桔迷：如果要改变温度要选什么系综a 桔迷(183331864) 21:27:12 ＮＶＴ 桔迷(183331864) 21:27:32 自己改变呗 娃娃(35861885) 21:28:06 只要选定这个ＮＶＴ系综了，温度就直接改变就行了吗？ 桔迷(183331864) 21:28:34 自己改温度 桔迷(183331864) 21:28:56 改完了算啊 体系结构稳定就行了 桔迷(183331864) 21:29:34 要做退火的话那要自己编程了。。我也不太懂 娃娃(35861885) 21:32:10 算体系的话，是不是做好先优化一下结构，然后，算性质的时候set up 里面Task选定Dynamics，properties里面算则要计算的性质就行，这样子对吗？ 桔迷(183331864) 21:33:20 还有步长 分子动力学很麻烦的 是动态过程你要等体系结构稳定为止 娃娃(35861885) 21:34:47 可以选择迭代的次数少一些吗？ 桔迷(183331864) 21:35:54 这不是迭代！！这是真实的运动轨迹计算，你去看一下分子动力学的书吧 娃娃(35861885) 21:36:23 奥 桔迷(183331864) 21:37:22 计算精度的设定需要一定的经验，这个我帮不了你 当然高精度应该没问题 只是耗时多些 娃娃(35861885) 21:37:45 奥，好的，谢谢啊 |
2楼2009-01-05 23:19:49
doudouding
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3楼2009-01-06 08:18:47
4楼2009-01-06 22:53:08