Hi Steve,

Thank you very much for your response. I have been trying the commands and

fix that you suggested and I have a couple of questions.

I tried the fix nve without and with temp/rescale to adjust the

temperature at 300 K. In both cases, the Ly dimension keeps growing. Also,

with fix nve, Lx, being periodic, does not change to accommodate the

thermal expansion. So, I specified the lattice constant at 300 K in the

lattice command.

I also tried the npt fix using NULL for the non-periodic directions. It

gave similar results.

For some reason, when I group together a few layers at the bottom

(Z-direction) and set their velocity to zero and use setforce to freeze

them, the Ly dimension stabilizes around the initial value. But I am not

sure if this is the right way of equilibrating the sample.

Please find below the input file that I used. It would be very helpful if

you could advise me on these issues.

Thanks again,

Yashashree

units metal

boundary p s s

atom_style atomic

# define simulation cell

lattice fcc 3.6357

region box block 0 9.797959 0 14.14213 0 86.6025404

create_box 5 box

lattice fcc 3.6357 orient x 1 -1 -2 orient y 1 1 0 orient z 1 -1 1

spacing 1.22475 1.41421 1.73205

create_atoms 1 box

# specify material and atom types

mass 1 63.55

pair_style eam

pair_coeff * * Cu_u3.eam

neighbor 2.0 bin

neigh_modify delay 5

# define boundary

region lower block INF INF INF INF INF 1.5

region upper block INF INF INF INF 48.5 INF

group lower region lower

group upper region upper

group boundary union lower upper

group mobile subtract all boundary

compute mobile_temp mobile temp

compute mobile_stress mobile stress/atom

compute stress mobile reduce sum c_mobile_stress[1]

c_mobile_stress[2] c_mobile_stress[3]

variable sxx equal c_stress[1]/vol

variable syy equal c_stress[2]/vol

variable szz equal c_stress[3]/vol

# equilibrate

velocity all create 600.0 5713354

fix 1 all nve

thermo 500

thermo_style custom step temp press lx ly lz v_sxx v_syy v_szz

thermo_modify lost warn norm yes

run 200000

Use fix nve for integration and the boundary command to

set your BC in xyz.

Steve

Hi,

I am new to LAMMPS and I am trying to equilibrate a Cu sample at 300 K,

with free surfaces in Y and Z directions and periodic in X direction. I

was wondering what ensemble or command to use for relaxation under these

BCs?

Any help would be deeply appreciated.

Thanks a lot,

Yashashree

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