AIMD simulation of a single water molecule

[Junbo Lu]

Hi,

    I am trying to use CP2K to run NVT simulation for a single water molecule. But I find that the temperature fluctuates seriously. I can not get equilibrium temperature. I set the temprature as 300 K in the input file. But the temperatures in energy file are:

......

      3070         1535.000000         0.002485140       523.162866214

      3071         1535.500000         0.002714404       571.426577303

      3072         1536.000000         0.003027088       637.251846392

      3073         1536.500000         0.003313526       697.551698813

      3074         1537.000000         0.003476351       731.829047391

      3075         1537.500000         0.003472049       730.923409677

      3076         1538.000000         0.003333209       701.695321066

      3077         1538.500000         0.003153364       663.834925398

      3078         1539.000000         0.003034701       638.854429382

      3079         1539.500000         0.003026153       637.054856190

      3080         1540.000000         0.003093963       651.330091922

......

    The last column is temperature. Could anyone help me? I would be very appreciated!

    With my best regards,

    Junbo

[suncsu]

Hi, 

    You need to provide the inp file so that we can know what the problem is.

    

    suncsu

------------------ 原始邮件 ------------------

发件人: "cp2k" <luju...@gmail.com>;

发送时间: 2021年1月15日(星期五) 晚上8:02

收件人: "cp2k"<cp...@googlegroups.com>;

主题: [CP2K:14555] AIMD simulation of a single water molecule

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[Krack Matthias (PSI)]

Hi

 

A single water molecule has only a few degrees of freedoms which results in large temperature fluctuations when potential energy is transferred to kinetic energy. Try a larger water sample, e.g. 32 molecules, since these fluctuations should average out more and more for larger systems.

 

Matthias

--

[Junbo Lu]

Hi,

  The attachments are the input file and energy file.

   With my best regards,

   Junbo

suncsu <5056...@qq.com> 于2021年1月15日周五 下午8:07写道：

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[Junbo Lu]

Hi Krack,

  Thank you very much for your comment. Yeah, I just need to do a test to calculate vibrational density of state for a single water molecule. Could I just do a NVE simulation fo a single water molecule.

   With my best regards,

   Junbo

Krack Matthias (PSI) <matthia...@psi.ch> 于2021年1月15日周五 下午10:13写道：

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[Marcella Iannuzzi]

Dear Junbo, 

You can, but as Matthias has said, the temperature fluctuations are going to be large

Regards

Marcella