GZ Zhang wrote:
Hi, ALL

I met a bizarre in a NVT simulation in which the initial temperature is ridiculously high.
Even though I specify the initial temperature to be 200 K.

; GENERATE VELOCITIES FOR STARTUP RUN
gen_vel                  = yes
gen_temp                 = 200.0
gen_seed                 = 173529

Energies (kJ/mol)
Bond LJ (SR) Coulomb (SR) Coul. recip. Potential 7.17894e+01 3.25101e+05 -3.75274e+05 - 3.13877e+05 -3.63978e+05
         Kinetic En.    Total Energy        Temperature      Pressure (bar)
    7.97000e+04   -2.84278e+05     1.00007e+04      2.75198e+06

The force field I used is called CLAYFF(http://www.sklogwiki.org/SklogWiki/index.php/CLAYFF_force_field), in which all atoms except hydroxyl groups interact through non-bonded vdW and electrostatic interactions. What's more strange is that after 5 ps, the system converted from a ordered layer structure into a disordered structure, like melting, although temperature goes to 200 K.

Any comments?


The combination of high temperature and really high pressure (beyond the normal +/- 1000 fluctuations) suggests that you have an unreasonable starting structure and/or broken topology. Atomic overlap (or bad parameters) will cause atoms to shoot wildly across the system, leading to large velocities and high temperature. In this case, you were fortunate that the whole system didn't explode but somehow continued.

-Justin

--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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