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# -------- WARNING: --------
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This directory contains some examples of all-atom simulations using the GAFF
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force field, prepared using moltemplate.
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This software is experimental, and the force-fields and equilbration protocols
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have not been tested carefully by me. There is no gaurantee that simulations
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prepared using moltemplate will reproduce the behavior of AmberTools/AMBER.
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# -------- REQUEST FOR HELP: --------
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If you notice a problem with these examples, please report it.
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Peer-review is the only way to improve this software (or any software).
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Other suggestions are also welcome!
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(Contact jewett.aij@gmail.com, 2013-12-01)
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Some force-fields (such as OPLSAA) can assign charge based on atom type.
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But AMBER simulations, charge is usually assigned using AmberTools which
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typically estimates partial charges using quantum chemistry.
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You must assign partial charges to each atom or LAMMPS will crash
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when it discovers your system has no charged particles.
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(To disable this, change the pair_style to lj/cut or something similar.)
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You have to assign charge manually, just as you would for an ordinary molecule.
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(For example, charges are explicitly assigned to each atom in these files:
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waterTIP3P+isobutane/moltemplate_files/isobutane.lt
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hexadecane/moltemplate_files/ch2group.lt
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hexadecane/moltemplate_files/ch3group.lt)
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(How you do this is up to you. In these examples, I obtained
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partial charges from the OPLSAA parameter file located here:
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http://dasher.wustl.edu/tinker/distribution/params/oplsaa.prm)
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--- Improper angles ---
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I am also uncertain whether the improper angle interactions generated by
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moltemplate are equivalent to those generated by AmberTools. (I think they are,
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but I am worried that I might have listed the atom types in the wrong order.)
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--- Bloated lammps input scripts ---
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LAMMPS input scripts prepared using moltemplate contain the entire contents
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of the GAFF force-field, even when simulating small systems with just a few
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This is harmless, but if you want to get rid of this extra information,
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follow the README instructions in the "optional_cleanup" directories.