[lammps-users] Problem with liquid lead

Hi all,
I tried to run a simulations of liquid Pb at 627K+ with tabulated Larson potential.NVE type calculation,but temperature in system dropped to ~ 310K(Solid Pb)and pressure was very high ~ 40kbar.The structure of lattice have remained(VMD visualisation). Does anyone can help me with this?How does the “liquid” Pb simulation make?

In.file:
units metal
dimension 3
boundary p p p

atom_style atomic
neighbor 5.0 bin
neigh_modify delay 10

lattice fcc 5.06
region box block 0 8 0 8 0 8
create_box 1 box
create_atoms 1 box

mass 1 207.2

pair_style table spline 20000001
pair_coeff 1 1 111.table er 10.005
pair_write 1 1 200 r 0.055 10.005 table.txt Pb

velocity all create 623.0 874287 mom yes dist gaussian
fix 1 all nve
#fix 2 all rdf 5000 rdf.out 1000 1 1

timestep 0.001
thermo 100
thermo_style multi

dump 1 all custom 1000 dump.pb id x y z

run 200000

Hi all,I tried to run a simulations of liquid Pb at 627K+ with
tabulated Larson potential.NVE type calculation,but temperature in
system dropped to ~ 310K(Solid Pb)and pressure was very high ~

hi ilya,

if you started from optimal crystal coordinates (i.e. 0K) this is
the expected behavior. about half of your initial kinetic energy
gets converted into potential energy. pick up your favorite text
book on molecular dynamics simulations and re-read the chapter
about equilibration and you will be enlightened. :wink:

40kbar.The structure of lattice have remained(VMD visualisation). Does
anyone can help me with this?How does the "liquid" Pb simulation make?

this is a common issue with melting a crystal. you have to consider
(substantial!) finite size effect and the impact of nucleation. thus
to melt a crystal, you have to first overshoot the temperature massively
and then gradually cool down. randomizing the initial coordinates
helps. again, this should be covered in any good book about MD.

cheers,
   axel.