[lammps-users] Silicon Melt

Hello all,

I am trying to use LAMMPS to simulate Stillinger Weber Silicon. I have put my input file below. I see, my system seems to be melting below the Melting point. Can anybody please help me in recognizing my mistake.

------Input File-----

units real
dimension 3
atom_style atomic

lattice fcc 5
region box block 0 10 0 10 0 10
create_box 1 box
create_atoms 1 box
mass 1 1.0

velocity all create 1690 41211 mom yes rot yes dist gaussian

pair_style sw
pair_coeff * * si.sw Si

neighbor 0.63 bin
neigh_modify delay 10

timestep 0.3830
run_style verlet

fix 1 all npt 1690 1690 500 xyz 0.0 0.0 200.0

thermo_style custom temp etotal vol press enthalpy
thermo 5

dump 1 all custom 100 ./data/Si_data.out tag type x y z

run 1000

May you be using the wrong epsilon in the potential? Check that epsilon=50 kcal/mol.
I think you may be using the parameter file that comes with lammps, that is for metal units (eV)

Hello Valeria,

Thanks for the reply… I am bit new to LAMMPS…
I am using si.sw which contains the following

Si Si Si 2.1683 2.0951 1.80 21.0 1.20 -0.333333333333
7.049556277 0.6022245584 4.0 0.0 0.0

Here epsilon is 2.1683 eV. Should I be changing this value.


Yes, if you use “units real” you must change the first parameter to 50 (conversion of 2.1683eV to kcal/mol).
All other parameters remain the same.


Dear Dr. Valeria,

Thanks for your reply on this conversion. Now i am doing the same. once i finish it i will get back to you with my result.