#===========================================================================#
# 2 particle microrheology test                                             #
#                                                                           #
# Run consists of 2 colloidal particles undergoing Brownian motion in a     #
#   thermal lattice-Boltzmann fluid.                                        #
#                                                                           #
# Here, gamma (used in the calculation of the particle-fluid interaction    #
#   force) is set by the user (gamma = 1.4692 for this simulation...this    # 
#   value has been calibrated a priori through simulations of the drag      # 
#   force acting on a single particle of the same radius).                  #
#                                                                           #
# Sample output from this run can be found in the file:                     # 
#   'microrheology_setgamma.out'                                            #
#===========================================================================#

units          nano
dimension      3
boundary       p p p
atom_style     molecular
read_data      data.two

#----------------------------------------------------------------------------
# Need a neighbor bin size smaller than the lattice-Boltzmann grid spacing   
#   to ensure that the particles belonging to a given processor remain inside
#   that processors lattice-Boltzmann grid.  
# The arguments for neigh_modify have been set to "delay 0 every 1", again
#   to ensure that the particles belonging to a given processor remain inside
#   that processors lattice-Boltzmann grid.  However, these values can likely
#   be somewhat increased without issue.  If a problem does arise (a particle
#   is outside of its processors LB grid) an error message is printed and 
#   the simulation is terminated.                                
#---------------------------------------------------------------------------- 
neighbor 0.3 bin
neigh_modify delay 0 every 1
neigh_modify exclude type 2 2
neigh_modify exclude type 2 1

#----------------------------------------------------------------------------
# Implement a hard-sphere interaction between the particles at the center of 
#   each colloidal object (use a truncated and shifted Lennard-Jones 
#   potential).
#----------------------------------------------------------------------------
pair_style	lj/cut 5.88
pair_coeff	* * 0.0 0.0 5.88
pair_coeff      1 1 100.0 5.238484463 5.88
pair_modify     shift yes

mass * 0.0002398
timestep 0.00045

#----------------------------------------------------------------------------
# ForceAtoms are the particles at the center of each colloidal object which  
#   do not interact with the fluid, but are used to implement the hard-sphere
#   interactions.       
# FluidAtoms are the particles representing the surface of the colloidal
#   object which do interact with the fluid.                               
#----------------------------------------------------------------------------
group ForceAtoms type 1
group FluidAtoms type 2

#---------------------------------------------------------------------------
# Create a lattice-Boltzmann fluid covering the simulation domain.
# This fluid feels a force due to the particles specified through FluidAtoms 
#   (however, this fix does not explicity apply a force back on to these 
#    particles...this is accomplished through the use of the rigid_pc_sphere 
#    fix).
# Use the LB integration scheme of Ollila et. al. (for stability reasons,
#   this integration scheme should be used when a large user set value for 
#   gamma is specified), a fluid viscosity = 1.0, fluid density= 0.0009982071, 
#   value for gamma=1.4692, lattice spacing dx=1.2, and mass unit, dm=0.003.
# Use a thermal lattice-Boltzmann fluid (temperature 300K, random number 
#   seed=2762).  This enables the particles to undergo Brownian motion in 
#   the fluid.
#----------------------------------------------------------------------------
fix   1 FluidAtoms lb/fluid 1 2 1.0 0.0009982071 setGamma 1.4692 dx 1.2 dm 0.003 noise 300.0 2762

#----------------------------------------------------------------------------
# Apply the force from the fluid to the particles, and integrate their 
#   motion, constraining them to move and rotate together as a single rigid 
#   spherical object.  
# Since both the ForceAtoms (central atoms), and the FluidAtoms (spherical
#   shell) should move and rotate together, this fix is applied to all of 
#   the atoms in the system.  However, since the central atoms should not
#   feel a force due to the fluid, they are excluded from the fluid force 
#   calculation through the use of the 'innerNodes' keyword.
# NOTE: This fix should only be used when the user specifies a value for 
#   gamma (through the setGamma keyword) in the lb_fluid fix. 
#----------------------------------------------------------------------------
fix   2 all lb/rigid/pc/sphere molecule innerNodes ForceAtoms 

#----------------------------------------------------------------------------
# To ensure that numerical errors do not lead to a buildup of momentum in the
#   system, the momentum_lb fix is used every 10000 timesteps to zero out the
#   total (particle plus fluid) momentum in the system.
#----------------------------------------------------------------------------
fix   3 all lb/momentum 10000 linear 1 1 1

#----------------------------------------------------------------------------
# Create variables containing the positions of the central atoms (these 
#   values should correspond to the center of mass of each composite 
#   colloidal particle), and output these quantities to the screen.
#----------------------------------------------------------------------------
variable x1 equal x[1]
variable y1 equal y[1]
variable z1 equal z[1]
variable x2 equal x[242]
variable y2 equal y[242]
variable z2 equal z[242]

thermo_style custom v_x1 v_y1 v_z1 v_x2 v_y2 v_z2
thermo       1

run	       2000000000
