relax.xm

来自「一个很好的分子动力学程序」· XM 代码 · 共 65 行

#######################################################################
#                                                                     #
#  Example:  Relaxing a lattice using CMD and QUENCH commands         #
#                                                                     #
#######################################################################
#                                                                     #
#    This example shows a method for relaxing a lattice to a low      #
#  energy state.  This is done by first performing a molecular        #
#  dynamics run at a moderate or low temperature (in this case 200K)  #
#  followed by a QUENCH command.  The QUENCH command acts like a      #
#  normal adiabatic (constant energy, with CLAMP set to -1)           #
#  molecular dynamics run only while the potential energy drops.      #
#  When the potential energy starts to rise, all the atom velocities  #
#  are automatically set to zero.  This removes the momentum that     #
#  would have carried the lattice uphill in potential energy,         #
#  allowing the lattice to beginning falling downhill again.          #
#                                                                     #
#######################################################################

# Relax lattice

# Read potential for nial
read ../nial.txt

# Make repeating box and lattice (in units of a0)
box 6 6 6
particle 2
1 0.25 0.25 0.25
2 0.75 0.75 0.75
dup 5   1 0 0
dup 5   0 1 0
dup 5   0 0 1

# Scale up to units of angstroms (2.8712 unit cell)
scale 2.8712

# Save energies from every dynamics step in file "timestep.e'
esave 10 relax.e

# Set particle masses (in atomic mass units)
select type 1
mass 58.71
select type 2
mass 26.982

# Set adiabtic simulation at starting temperature of 200K
clamp -1
itemp 200

#  This may not be the optimum step size
dtime  1e-15

#  Equilibrate at 200K for 500 steps
write rcv relax.rcv
repeat 5
   cmd 100
   write rcv +relax.rcv
end

#  Quench for 500 steps
repeat 5
   quench 100
   write rcv +relax.rcv
end