# Initialization
units           lj
dimension       3
boundary        p p s
atom_style      bond

# Ensure ghost atoms store velocities for DPD pair style
comm_modify     vel yes
#comm_modify     cutoff 2.5

# Define variables for upper and lower z-values of the fluid region
variable        fluid_z_up equal 15.25          # upper z value of fluid
variable        fluid_z_down equal -15.25       # lower z value of fluid
variable        xl equal -30
variable        xh equal 30
variable        yl equal -1.5
variable        yh equal 1.5
# Define new variables for adjusted z-values for simulation box
variable        simbox_z_up equal ${fluid_z_up}+2
variable        simbox_z_down equal ${fluid_z_down}-2

# Define variables for adjusted z-values for plates
variable        lower_plate_z_up equal ${fluid_z_down}
variable        lower_plate_z_down equal ${fluid_z_down}-2
variable        upper_plate_z_down equal ${fluid_z_up}
variable        upper_plate_z_up equal ${fluid_z_up}+2

# Create simulation box with z boundaries based on fluid_z_up and fluid_z_down
region          simbox block v_xl v_xh v_yl v_yh v_simbox_z_down v_simbox_z_up
create_box      2 simbox

# Set masses for atom types
mass            1 1.0  # Mass for plate particles (Group A)
mass            2 1.0  # Mass for fluid particles (Group B)

# Define regions for plates, fluid, and spherical wall
region          lower_plate block v_xl v_xh v_yl v_yh v_lower_plate_z_down v_lower_plate_z_up
region          upper_plate block v_xl v_xh v_yl v_yh v_upper_plate_z_down v_upper_plate_z_up
region          fluid_actual block v_xl v_xh v_yl v_yh v_fluid_z_down v_fluid_z_up


# Create atoms for plates with high density
lattice         fcc 6
create_atoms    1 region lower_plate
create_atoms    1 region upper_plate

# Create atoms for fluid with lower density
lattice         fcc 4
create_atoms    2 region fluid_actual


#group by type
group           walls type 1
group           fluid type 2

# Define DPD settings
pair_style      dpd 1.0 1.0 12345  #  standard

#Set dpd coefficient
pair_coeff      1 1 0.0 4.5 1.0  # No interaction between wall particles
pair_coeff      1 2 9.68 4.5 1.0 # Interaction between wall and fluid particles,
pair_coeff      2 2 18.75 4.5 1.0 # Interaction between fluid particles

# Freeze wall particles
fix             freeze_walls walls setforce 0.0 0.0 0.0

# Reflective boundary conditions for fluid particles at plate boundaries
fix             wall_lower fluid wall/reflect zlo v_fluid_z_down
fix             wall_upper fluid wall/reflect zhi v_fluid_z_up

# Apply a constant force to fluid particles to simulate gravity
variable        grav_x equal 0.02  # Adjust this value to set the strength of the gravitational field
fix             gravity fluid addforce v_grav_x 0.0 0.0

# Neighbor list settings
neighbor        0.3 bin  # Increase the skin distance
neigh_modify    delay 5 check yes

# Initial velocities for fluid particles
velocity        fluid create 1.0 12345


# Time integration using NVT for thermostatting
fix             2 all nve  # Plain velocity verlet integration

# Compute temperature for fluid region
compute         fluid_temp fluid temp/region fluid_actual

# Output settings
thermo          1000
thermo_style    custom step temp c_fluid_temp pe ke etotal press
dump            2    all custom 1000 dumpvelforce.lammpstrj id type x y z vx vy vz fx fy fz 
restart         100000 restart.lammpstrj 

# Run settings
timestep        0.01  # Reduce the time step for stability
run             10000000