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Re: [lammps-users] Silicon bulk Melting Point
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Re: [lammps-users] Silicon bulk Melting Point


From: Hao Chen <haochen@...258...>
Date: Mon, 24 Jul 2017 15:41:47 -0500

Thanks, Axel. Yes, you are totally correct. The melting can be dependent on the size and setup of the simulations. So either you can try to change the size or setup. Or you can find some paper which has those data for different potential. Thanks.

On Mon, Jul 24, 2017 at 3:32 PM, Axel Kohlmeyer <akohlmey@...24...> wrote:
On Mon, Jul 24, 2017 at 3:20 PM, Hao Chen <haochen@...258...> wrote:
> Maybe you can try different potentials. From my knowledge, maybe SW
> potential would be better for melting for silicon. Hope this can be useful
> to you. Or you can try reaxff potential.

this won't really help much, because the method of determining the
melting point from raising the temperature and observing energies is
flawed. it is dependent on system size, how quickly you raise the
temperature, the type of thermostat, and whether you raise or lower
the temperature.

if you shop around until you find a potential, that gives the desired
result for the given conditions, you just are getting the desired
answer for the wrong reason.

axel.

>
> On Mon, Jul 24, 2017 at 1:57 PM, Djelel Djelloul <bdjelel1398@...24...>
> wrote:
>>
>> Dear All,
>>
>> I tried  to calculate the melting point for the  Silicon bulk  with the
>> parameters bellow but it gave me a wrong value for the melting point(about
>> 2000) , but the right value (literature) is about 1600.
>>
>> please,whre is the problem, in the input file ?
>>
>> =============================================================
>> # ---------- Initialize Simulation ---------------------
>> clear
>> units metal
>> dimension 3
>> boundary p p p
>> atom_style atomic
>> atom_modify map array
>>
>> # ---------- Create Atoms ---------------------
>> lattice diamond 5.43
>> region box block 0 6 0 6 0 6 units lattice
>> create_box 1 box
>>
>> create_atoms 1 box
>> mass 1 28.085  ##Silicon
>>
>> # ---------- Define Interatomic Potential ---------------------
>>
>> pair_style edip
>> pair_coeff * * Si.edip Si
>>
>> # 0.63 is sufficient. but ....!
>> neighbor 3.0 bin
>> neigh_modify delay 10 check yes
>>
>> # ----------  create inital velocities at 1000 k --------------------
>> velocity        all create 400 45827325 mom yes rot yes dist uniform
>>
>>
>> # Nose-Hoover thermostat (annealing bulk from 1000 to 3000 K)
>> fix             nvt1 all nvt temp 400.0 400.0 0.01
>> timestep        0.0005
>>
>> # ----------  display each 1000 step  --------------------
>> thermo_style custom step temp pe ke etotal
>> thermo 100
>>
>> # ------------ just some simple calculation ---------------------
>> variable  TEM    equal temp
>> variable  TE     equal etotal
>> variable  KE     equal ke
>> variable  PE     equal pe
>>
>> #---------------- output data file for plotting --------------------------
>> fix temp_out all ave/time 100 10 1000 v_TEM v_PE v_KE v_TE ave window 2
>> file out_400
>>
>> #-------------- a movie of what happens. why not!  ---------------------
>> dump    1 all custom 100 si_xyz_bulk.out id type x y z
>>
>>
>> run 500000
>>
>> print "All done!"
>>
>>
>>
>>
>>
>> ==============================================================
>>
>> Best Regards
>>
>>
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>
>
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--
Dr. Axel Kohlmeyer  akohlmey@...43...4...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.