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lammps/tools/moltemplate/examples/coarse_grained/membrane_BranniganPRE2005/moltemplate_files/CGLipidBr2005Orig.lt
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CGLipidBr2005Orig.lt
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# Note:
#
# This example may require additional features to be added to LAMMPS. If
# LAMMPS complains about an "Invalid pair_style", then download copy the
# "additional_lammps_code" from moltemplate.org, unpack it into your LAMMPS
# "src" directory and recompile LAMMPS.
#
# -------- Description --------
#
# This example contains an implementation of the DPPC lipid bilayer described in
# G. Brannigan, P.F. Philips, and F.L.H. Brown,
# Physical Review E, Vol 72, 011915 (2005)
# and:
# M.C. Watson, E.S. Penev, P.M. Welch, and F.L.H. Brown
# J. Chem. Phys. 135, 244701 (2011)
#
# As in Watson(JCP 2011), rigid bond-length constraints have been replaced
# by harmonic bonds.
#
# --- DLPC lipids ---
# A truncated version of the DPPC lipid (named "DLPC") has also been added.
# Unlike the original "DPPC" molecule model, "DLPC" has not been carefully
# parameterized to reproduce the correct behavior in a lipid bilayer/mixture.
# (You may need to stiffen the bond-angle forces to make it behave correctly,
# but I did not do this here.)
#
# Units:
#
# The "epsilon" parameter in their model is approximately 2.75 kJ/mole
# ( = 0.657265774378585 kCal/mole, using 1kCal=4.184kJ)
# The "sigma" parameter corresponds to 7.5 angstroms.
#
#
# The new DLPC model is a truncated version of DPPC,
# (Its behaviour has not been rigorously tested.)
CGLipidBr2005 {
write_once("In Init") {
# -- Default styles for "CGLipidBr2005" --
units real
atom_style full
# (Hybrid force field styles were used for portability.)
bond_style hybrid harmonic
angle_style hybrid cosine/delta # <- used in the original article
#angle_style hybrid harmonic # <- prevents unphysical acute angle turns
# Explanation:
# angle_style cosine/delta: U(theta) = k*(1-cos(theta-theta0))
# angle_style harmonic: U(theta) = k*(theta-theta0)^2
dihedral_style none
improper_style none
pair_style hybrid table linear 1130 &
lj/charmm/coul/charmm/inter es4k4l 14.5 15
pair_modify mix arithmetic
special_bonds lj 0.0 0.0 1.0 # turn off pairs if "less than 3 bonds"
}
DPPC {
write("Data Atoms") {
$atom:h $mol:. @atom:head 0.0 0.00 0.00 33.75 # DPPC head atom
$atom:i $mol:. @atom:../int 0.0 -1.00 0.00 26.25
$atom:t1 $mol:. @atom:../tail 0.0 1.00 0.00 18.75
$atom:t2 $mol:. @atom:../tail 0.0 -1.00 0.00 11.25
$atom:t3 $mol:. @atom:../tail 0.0 1.00 0.00 3.75
}
write("Data Bonds") {
$bond:b1 @bond:../backbone $atom:h $atom:i
$bond:b2 @bond:../backbone $atom:i $atom:t1
$bond:b3 @bond:../backbone $atom:t1 $atom:t2
$bond:b4 @bond:../backbone $atom:t2 $atom:t3
}
write("Data Angles") {
$angle:a1 @angle:../backbone $atom:h $atom:i $atom:t1
$angle:a2 @angle:../backbone $atom:i $atom:t1 $atom:t2
$angle:a3 @angle:../backbone $atom:t1 $atom:t2 $atom:t3
}
# Define properties of the local (lipid-specific) atom:head type atom:
write_once("Data Masses") {
@atom:head 200.0
}
write_once("In Settings") {
pair_coeff @atom:head @atom:head lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
pair_coeff @atom:../int @atom:head lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
pair_coeff @atom:../tail @atom:head lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
}
} #DPPC
DLPC {
write("Data Atoms") {
$atom:h $mol:. @atom:head 0.0 0.00 0.00 30.00 # DLPC head atom
$atom:i $mol:. @atom:../int 0.0 -1.00 0.00 22.50
$atom:t1 $mol:. @atom:../tail 0.0 1.00 0.00 15.00
$atom:t2 $mol:. @atom:../tail 0.0 -1.00 0.00 7.50
}
write("Data Bonds") {
$bond:b1 @bond:../backbone $atom:h $atom:i
$bond:b2 @bond:../backbone $atom:i $atom:t1
$bond:b3 @bond:../backbone $atom:t1 $atom:t2
}
write("Data Angles") {
$angle:a1 @angle:../backbone $atom:h $atom:i $atom:t1
$angle:a2 @angle:../backbone $atom:i $atom:t1 $atom:t2
}
# Define properties of the local (lipid-specific) atom:head type atom:
write_once("Data Masses") {
@atom:head 200.0
}
write_once("In Settings") {
pair_coeff @atom:head @atom:head lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
pair_coeff @atom:../int @atom:head lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
pair_coeff @atom:../tail @atom:head lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
}
} #DLPC
# Particles and properties shared by all lipid types:
write_once("Data Masses") {
@atom:int 200.0
@atom:tail 200.0
}
write_once("In Settings") {
# -- Default settings/parameters for "CGLipidBr2005" --
# (Hybrid bond & angle styles were used for portability.)
# As in Watson(JCP 2011), rigid bond-length constraints
# have been replaced by harmonic bonds.
# The k_theta parameter should lie in between 5*epsilon and 10*epsilon.
bond_coeff @bond:backbone harmonic 116.847 7.5 #<--2*5000*eps/sig^2
}
write_once("In Settings") {
# cosine/delta: U(theta) = k*(1-cos(theta-theta0))
angle_coeff @angle:backbone cosine/delta 4.60086042 180 #<-- 7*eps
## Alternately, to stiffen the bond-angles, try this:
##angle_coeff @angle:backbone cosine/delta 6.57265774 180 #<-- 10*eps
## harmonic: U(theta) = k*(theta-theta0)^2 not (k/2)*(theta-theta0)^2
##angle_coeff @angle:backbone harmonic 9.85898661 180 #<-->30*eps
}
# Note: You may want to use a stiffer bond-angle than the original
# Brannigan&Brown 2005 paper if you want to mix two different lipids together.
# (The mixture of lipids introduces a great deal of disorder into the bilayer
# which would not be present in a DPPC bilayer. This caused pores to form
# in my simulations. But increasing the angle stiffness prevents this.)
write_once("In Settings") {
# The interaction of "atom:int" with other "atom:int" atoms is given by
# epsilon*(0.4*(sigma/r)^12 - 3.0*(sigma/r)^2), shifted and cutoff at
# r=3*sigma. This was implemented using pair_style table.
# Unfortunately, mixing lj/charmm and "table" pair styles in the same
# simulation is very inneficient.
pair_coeff @atom:int @atom:int table table_int.dat INT
# The interaction of tail beads with eachother is given by the formula below
# and with other atoms ...using Lorenz-Berthelot and "repulsive wins" rules:
# epsilon*(0.4*(sigma/r)^12 - 1.0*(sigma/r)^6),
pair_coeff @atom:tail @atom:tail lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 -1
pair_coeff @atom:int @atom:tail lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 -1
# The interaction between head beads from different types of lipids
# is (currently) repulsive:
pair_coeff @atom:DPPC/head @atom:DLPC/head lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
} # write_once("In Settings")
# Note: I divided epsilon by 4 to get "0.1643" because we are using the
# "es4k4l" coeffstyle, corresponding to U(r)=eps(4*K*(s/r)^12 + 4*L*(s/r)^6)
# (The "es4k4l" coeffstyle is the default.) Using this convention makes it
# easier to mix this coarse-grained lipid model with other molecular models.
} # CGLipidBr2005
# Note: This example has not been optimized for speed.
#
# Unfortunately, using both lj/charmm and "table" pair styles in the same
# simulation seems to be very inneficient. (The simulation is twice as slow
# as using only the "lj/charmm" pair styles for every pairwise interaction,
# ...and about 25% slower than using "table" for every pairwise interaction.
# However the lennard-jones pair styles support mixing, so we use them to
# make it easier to run these molecules with other molecules which don't use
# pair_table. I felt that portability was worth the extra 25% slow down.)
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