# GCMC for CO2 molecular fluid, rigid/small dynamics
# Rigid CO2 TraPPE model
# [Potoff and J.I. Siepmann, Vapor-liquid equilibria of
# mixtures containing alkanes, carbon dioxide and
# nitrogen AIChE J., 47,1676-1682 (2001)].

# variables available on command line

variable        mu index -8.1
variable        disp index 0.5
variable        temp index 338.0
variable        lbox index 10.0
variable        spacing index 5.0

# global model settings

units           real
atom_style      full
boundary        p p p
pair_style      lj/cut/coul/long  14
pair_modify     mix arithmetic tail yes
kspace_style    ewald 0.0001
bond_style      harmonic
angle_style     harmonic

# box, start molecules on simple cubic lattice

lattice         sc ${spacing}
region          box block 0 ${lbox} 0 ${lbox} 0 ${lbox} units box
create_box      2 box                       &
                bond/types 1                &
                angle/types 1               &
                extra/bond/per/atom 2       &
                extra/angle/per/atom 1      &
                extra/special/per/atom 2
molecule        co2mol CO2.txt
create_atoms    0 box mol co2mol 464563 units box

# rigid CO2 TraPPE model

pair_coeff      1   1  0.053649   2.8
pair_coeff      2   2  0.156973   3.05
bond_coeff      1       0       1.16
angle_coeff     1       0       180

# masses

mass 1 12.0107
mass 2 15.9994

# MD settings

group           co2 type 1 2
neighbor        2.0 bin
neigh_modify    every 1 delay 10 check yes
velocity        all create ${temp} 54654
timestep        1.0

# rigid constraints with thermostat

fix             myrigid co2 rigid/small molecule mol co2mol

# dynamically update  fix rigid/nvt/small temperature ndof
fix_modify      myrigid dynamic/dof yes

# gcmc

variable        tfac equal 5.0/3.0 # (3 trans + 2 rot)/(3 trans)
fix             mygcmc co2 gcmc 100 100 0 0 54341 ${temp} ${mu} ${disp} mol &
                co2mol tfac_insert ${tfac} group co2 rigid myrigid

# atom counts

variable        carbon atom "type==1"
variable        oxygen atom "type==2"
group           carbon dynamic co2 var carbon
group           oxygen dynamic co2 var oxygen
variable        nC equal count(carbon)
variable        nO equal count(oxygen)

# output

variable        tacc equal f_mygcmc[2]/(f_mygcmc[1]+0.1)
variable        iacc equal f_mygcmc[4]/(f_mygcmc[3]+0.1)
variable        dacc equal f_mygcmc[6]/(f_mygcmc[5]+0.1)
variable        racc equal f_mygcmc[8]/(f_mygcmc[7]+0.1)

# dynamically update default temperature ndof
compute_modify  thermo_temp dynamic/dof yes

thermo_style    custom step temp press pe ke density atoms v_iacc v_dacc v_tacc v_racc v_nC v_nO
thermo          1000

# run

run             20000