This section covers the Siepmann-Martin-Mundy-Klein (SMMK) force field for branched alkanes as it is implemented
into the towhee_ff_SMMKmain file in the ForceFields directory. All of the Towhee atom types for this force field
are listed, along with a short description of their meanings.
SMMKmain uses a 'Lennard-Jones' classical_potential and the 'Geometric' classical_mixrule.
Unlike its predecessor (SKS) the SMMKmain force field uses tail corrections,
and was originally used with a 13.8 Angstrom cutoff.
The SMMKmain forcefield is an extension of the SKS force field for linear alkanes and
was immediately supplanted by similar parameters included in the same paper
(see SMMK Note Added in Proof and eventually replaced by the
TraPPE-UA force field.
Any discrepencies (especially typos) from the published force field values are the sole
responsibility of Marcus G. Martin, and I welcome feedback on how this
implementation compares with other programs.
References for SMMK Main
Most of the nonbonded parameters and detailed results for the SMMK Main force field are found in the main text of the
This is a fully flexible model where the intramolecular terms for all of the atoms, and some special One-Five
nonbonded terms for CH3methyl groups are taken from.
SMMK Main in Towhee
The official force field name for SMMK Main in Towhee is 'SMMKmain'. Here
I list all of the atom names for use in the towhee_input file, along with a brief description.
Please note that the capitalization and spacing pattern is important and must be followed exactly
as listed here.
- 'CH3long' methyl group (C plus 3 bonded H as a united-atom) on an n-alkane of C4 or longer,
or on an alkyl side-chain of length propyl or longer.
- 'CH3ethyl' methyl group (C plus 3 bonded H as a united-atom) on an ethyl side-chain.
- 'CH3methyl' methyl group (C plus 3 bonded H as a united-atom) on an methyl side-chain.
- 'CH2' methylene group (C plus 2 bonded H as a united-atom).
- 'CH' methine group (C plus 1 bonded H as a united-atom).
- 'C' quaternary carbon.
There are no coulombic interactions for this force field.
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