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This example shows how to build a multicomponent spherical vesicle.
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The lipid bilayer is composed of two different lipids (DPPC and DLPC).
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The vesicle also contains trans-membrane protein inclusions.
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The coordinates for the vesicle are constructed by PACKMOL (see below).
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The DPPC lipid model is described here:
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G. Brannigan, P.F. Philips, and F.L.H. Brown,
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Physical Review E, Vol 72, 011915 (2005)
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(The DLPC model is a truncated version of DPPC. Modifications discussed below.)
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The protein model is described here:
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G. Bellesia, AI Jewett, and J-E Shea,
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Protein Science, Vol19 141-154 (2010)
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--- PREREQUISITES: ---
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1) This example requires PACKMOL. You can download PACKMOL here:
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http://www.ime.unicamp.br/~martinez/packmol/
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(Moltemplate does not come with an easy way to generate spherically-symmetric
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structures, so I used the PACKMOL program to move the molecules into position.)
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2) This example requires the "dihedral_style fourier", which is currently
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in the USER-MISC package. Build LAMMPS with this package enabled using
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before compiling LAMMPS.
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(See http://lammps.sandia.gov/doc/Section_start.html#start_3 for details.)
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3) This example may require additional features to be added to LAMMPS.
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If LAMMPS complains about an "Invalid pair_style", then
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a) download the "additional_lammps_code" from
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http://moltemplate.org (upper-left corner menu)
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c) copy the .cpp and .h files to the src folding of your lammps installation.
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d) (re)compile LAMMPS.
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------ Details -------
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This example contains a coarse-grained model of a 4-helix bundle protein
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inserted into a lipid bilayer (made from a mixture of DPPC and DLPC).
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The coarse-grained protein is described in:
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G. Bellesia, AI Jewett, and J-E Shea, Protein Science, Vol19 141-154 (2010)
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Here we use the "AUF2" model described in that paper.
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(The hydrophobic beads face outwards.)
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-- Memebrane Model: --
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The DPPC lipid bilayer described in:
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G. Brannigan, P.F. Philips, and F.L.H. Brown,
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Physical Review E, Vol 72, 011915 (2005)
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M.C. Watson, E.S. Penev, P.M. Welch, and F.L.H. Brown
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J. Chem. Phys. 135, 244701 (2011)
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As in Watson(JCP 2011), rigid bond-length constraints
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have been replaced by harmonic bonds.
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A truncated version of this lipid (named "DLPC") has also been added.
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The bending stiffness of each lipid has been increased to compensate
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for the additional disorder resulting from mixing two different types
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of lipids together. (Otherwise pores appear.)
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Unlike the original "DPPC" molecule model, the new "DPPC" and "DLPC" models
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have not been carefully parameterized to reproduce the correct behavior in
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a lipid bilayer mixture.
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-- Interactions between the proteins and lipids --
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This is discussed in the "system.lt" file.
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--- Building the files necessary to run a simulation in LAMMPS ---
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Type these commands into the shell.
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(Each command could take several hours.)
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packmol < step1_proteins.inp # This step determines the protein's location
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packmol < step2_innerlayer.inp # this step builds the inner monolayer
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packmol < step3_outerlayer.inp # this step builds the outer monolayer
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step 2) Run MOLTEMPLATE
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Type these commands into the shell.
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(This could take up to 10 minutes.)
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moltemplate.sh system.lt -xyz ../system.xyz
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mv -f system.in* system.data ../
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cp -f table_int.dat ../
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--- Running LAMMPS ---
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Type these commands into the shell.
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(This could take days.)
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lmp_linux -i run.in.min # Minimize the system (important, and very slow)
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lmp_linux -i run.in.nvt # Run a simulation at constant volume
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If you have compiled the MPI version of lammps, you can run lammps in parallel:
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mpirun -np 4 lmp_linux -i run.in.min
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mpirun -np 4 lmp_linux -i run.in.nvt
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(Assuming you have 4 cores, for example.)