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


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Mon, 24 Jul 2017 15:18:25 -0400

On Mon, Jul 24, 2017 at 2:57 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.

does "literature" here mean the experimental literature, or the paper
describing the potential you are using?

> please,whre is the problem, in the input file ?

the problem is in your thinking.

have you tried the same simulation with a different number of
timesteps, i.e. a different rate of heating?
have you tried the same simulation starting from a high temperature
and recording the point where the system solidifies?
have you tried the same two simulations with different system sizes?

if you do this, you should learn a few things, that are well
understood and documented in the literature. it boils down to the
fact, that activated processes on the atomic scale are different than
on the macroscopic scale, so you cannot apply the same methodology. it
has been discussed on this very mailing list, that the most reliable
way to determine the melting point at the atomic scale is to do a
coexistence simulation where you monitor the size of the liquid and
the solid phase. if they remain the same, and not one is growing at
the expense of the other, you have the melting point.

axel.


>
> =============================================================
> # ---------- 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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>



-- 
Dr. Axel Kohlmeyer  akohlmey@...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.