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lammps/examples/USER/qtb/alpha_quartz_qbmsst/alpha_quartz_qbmsst.in
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alpha_quartz_qbmsst.in
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## This script first uses fix qtb to equilibrate alpha quartz structure to an initial state with quantum nuclear correction and then simulate shock induced phase transition through the quantum thermal bath multi-scale shock technique
variable x_rep equal 2 #plot is made with x_rep = 8 #x-direction replication number
variable y_rep equal 1 #plot is made with y_rep = 5 #y-direction replication number
variable z_rep equal 4 #plot is made with z_rep = 15 #z-direction replication number
variable cut_off equal 10.0 #Cut-off distance for the Buckingham term (Angstrom in metal units)
variable pressure equal 1.03125 #Initial state pressure (bar in metal units)
variable temperature equal 300.0 #Initial state quantum temperature (K in metal units)
variable delta_t equal 1.0e-3 #MD timestep length (ps in metal units)
variable damp_qtb equal 1 #1/gamma where gamma is the friction coefficient in quantum thermal bath (ps in metal units)
variable v_msst equal 78.0 #Shock velocity (Angstrom/ps in metal units)
variable q_msst equal 40.0 #Box mass-like parameter in the MSST (mass^2/length^4, where mass=grams/mole and length=Angstrom in metal units)
variable tscale_msst equal 0.05 #Temperature reduction parameter in the MSST (unitless)
variable eta_qbmsst equal 1.0 #Coupling constant between the shock and the quantum thermal bath (unitless constant)
## This part uses fix qtb to prepare alpha-quartz with quantum nuclear correction of the initial state
include alpha_quartz_qtb.mod
## This part demonstrates how to retart fix qbmsst during any stage of the shock simulation.
## PPPM may break down when compression ratio becomes extremely large. One can always use this restart technique to resume the shock simulation.
#Compression restart 1
reset_timestep 0
#Beta is the number of time steps between each update of the quantum bath temperature. Setting a larger beta can reduce thermal flactuations.
fix shock all qbmsst z ${v_msst} q ${q_msst} tscale ${tscale_msst} damp ${damp_qtb} f_max 120 N_f 100 seed 35082 eta ${eta_qbmsst} beta 5 T_init ${temperature}
fix_modify shock energy yes
variable dhug equal f_shock[1]
variable dray equal f_shock[2]
variable lgr_vel equal f_shock[3]
variable lgr_pos equal f_shock[4]
variable T_qm equal f_shock[5] #Temperature with quantum nuclear correction
thermo_style custom step v_T_qm press etotal vol lx ly lz pzz v_dhug v_dray v_lgr_vel v_lgr_pos
thermo 100
timestep ${delta_t}
run 1000
write_restart restart.1000
#Compression restart 2
#Read restart file and load potential again
clear
read_restart restart.1000
include alpha_quartz_potential.mod
#Use the same fix id and add no tscale if the system is already compressed
fix shock all qbmsst z ${v_msst} q ${q_msst} tscale 0.0 damp ${damp_qtb} f_max 120 N_f 100 seed 35082 eta ${eta_qbmsst} beta 5 T_init ${temperature}
fix_modify shock energy yes
variable dhug equal f_shock[1]
variable dray equal f_shock[2]
variable lgr_vel equal f_shock[3]
variable lgr_pos equal f_shock[4]
variable T_qm equal f_shock[5] #Temperature with quantum nuclear correction
thermo_style custom step v_T_qm press etotal vol lx ly lz pzz v_dhug v_dray v_lgr_vel v_lgr_pos
thermo 100
timestep ${delta_t}
restart 1000 restart
run 10000 #10 ps
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