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Re: [lammps-users] Melting of Amorphous Silica
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Re: [lammps-users] Melting of Amorphous Silica


From: "S Arun Srikant Sridhar" <ss3763@...1685...>
Date: Wed, 14 Jun 2017 04:38:04 -0400

Hello pooja.

  want to simulate amorphous silica for which I will be melting and quenching the amorphous phase with the BKS potential. 

Before simulating you have to equilibrate the system. 
After equilibration the system has to be heated to 5000 K (Check order parameters  rdf, autocorrelation..)
Check what happens to the density and other thermodynamic outputs and also observe the box dimensions. 
From your lammps input script I see that you are in the equilibration stage and you have not yet started the quenching process. 

 I performed simulation with NVE ensemble and then also tested with fix NVT and fix NPT both. But for all the cases the temperature of the system was increasing.
I suspect this may be due to bad geometry. 
Please minimize the system before you start the equilibration to eliminate close contacts. Then use fix nve, nvt with langevin and switch to npt.



Good luck 
Arun  




On 06/14/17, Rana Ali <ranadeepu2017@...24...> wrote:
Dear All,
  I want to simulate amorphous silica for which I will be melting and quenching the amorphous phase with the BKS potential. I am performing melting at 5000 K. Then I want to quench the system from 5000 K to 300K at rate of 5K/ps. However, when I perform melting process at 5000K, I see the temperature of the system is not fixed to 5000K but keep on increasing. I performed simulation with NVE ensemble and then also tested with fix NVT and fix NPT both. But for all the cases the temperature of the system was increasing. My system contains 795 atoms (265 SiO2 molecules) that were randomly placed in a box of 20A*20A*30A. My Lammps input file and datafile are written below  .. Does anybody have any idea about what this problem may be due to?

With thanks and regards,
Pooja
     
 ##### Lammps input file

dimension 3
boundary p p p

units  real
atom_style charge
neighbor 0.3 bin
neigh_modify delay 1

read_data  FilledConfig.data

# Buck potentials
kspace_style pppm 1.0e-4

pair_style buck/coul/long 8 10

## Si type 1, O type 2

pair_coeff 1 1      0.00000   0.100000      0.000000
pair_coeff 1 2 415172.94230   0.205205   3079.435324
pair_coeff 2 2  32025.59145   0.362319   4035.561250


# initial velocities
velocity all create 5000.0 4928459

#fix             1 all nve
#fix             1  all  nvt temp  5000.0 5000.0 100.0
#fix             2  all  npt temp  5000.0 5000.0 100.0 iso 0.00 0.00 1000.0
fix              2  all  npt temp  5000.0 5000.0 100.0 iso 1.00 1.00 1000.0

# Run
timestep    0.0005# Custom data file for mixture of,     SiO2,
thermo 100
thermo_modify temp new

dump             6 all custom 1000  Bk5silica.dump id type x y z
restart          10000  restart
run 1000000


>>>>>>>>>..  Datafile .........

       795  atoms
           2  atom types

    0.00000000000000    27.00000000000000 xlo xhi
    0.00000000000000    27.00000000000000 ylo yhi
    0.00000000000000    37.00000000000000 zlo zhi

 Masses

           1   28.0855000000000
           2   15.9994000000000

 Atoms

      1           1     2.40000000000000   21.19574979863687   26.56314348998866   16.60392077187158
      2           2    -1.20000000000000   20.92168213846226   25.53602206331959   15.51052093332094
      3           2    -1.20000000000000   21.47366081769066   27.59632008729189   17.69062596179387
      4           1     2.40000000000000    4.03179762537331   10.97965995043920    7.14349606133526
      5           2    -1.20000000000000    3.65206065147185   10.83498298398472    8.61335425873001
      6           2    -1.20000000000000     793           1     2.40000000000000    4.71131037495489   19.71224239165641   24.08558656679686

.............................
.........................
793           1     2.40000000000000    4.71131037495489   19.71224239165641   24.08558656679686
    794           2    -1.20000000000000    4.31561499933014   20.34039317191318   22.75349554836349
    795           2    -1.20000000000000    5.10559026902073   19.09271841574135   25.42213061542843
4.42100242879972   11.12482182623187    5.67616370759368