Energy minimization

LAMMPS LAMMPS Mailing List Mirror
1

Hello,

I am trying to preform an energy minimization of a B2 phase ZrCu crystal, so that I can find the average energy of both the Zr and Cu atoms in the crystal. In the LAMMPS code below I am trying to do a conjugate gradient minimization, but also need to allow the volume of the box to relax so that the pressure tends to zero.

My questions are: Is the “fix box/relax” command correct to use if I want to allow the volume to be able to change while the minimization is happening? Should I be using a “fix npt” instead and specify a temperature? The code below seems to cause the pressure to fluctuate widely. This is confusing me.

units metal
atom_style atomic
boundary p p p
read_data Zr2Cu.initial
mass 2 63.55
mass 1 91.22
pair_style eam/alloy
pair_coeff * * ZrCu.eam.alloy Zr Cu
neighbor 1.6 bin
neigh_modify every 1 delay 5 check yes
group zir type 1
group cup type 2
compute energyZr zir pe/atom
compute zr_pe zir reduce sum c_energyZr
compute energyCu cup pe/atom
compute cu_pe cup reduce sum c_energyCu
reset_timestep 0
fix 1 all box/relax iso 0.0 vmax 0.001
thermo 1
thermo_style custom step temp press etotal pe c_zr_pe c_cu_pe
min_style cg
minimize 1.0e-25 1.0e-25 5000 10000

Thanks,

Sven

2

Hello,

I am trying to preform an energy minimization of a B2 phase ZrCu crystal,
so that I can find the average energy of both the Zr and Cu atoms in the
crystal. In the LAMMPS code below I am trying to do a conjugate gradient
minimization, but also need to allow the volume of the box to relax so that
the pressure tends to zero.

My questions are: Is the "fix box/relax" command correct to use if I want
to allow the volume to be able to change while the minimization is
happening? Should I be using a "fix npt" instead and specify a temperature?
The code below seems to cause the pressure to fluctuate widely. This is
confusing me.

Then you need to read more about the basics of the algorithms you are
trying to use. Read the manual as well instead of turning to the list for
emotional support. What does the manual says about box/relax? Do you know
what npt even means? Your confusion wont go away until you read and learn
by experimenting. Trusting the people here blindly is not different from
believing in the after life, witches, etc.
Carlos

3

Fix npt does not operate during a minmization. Temperature

is also meaningless during a minimization.

Steve