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                    PARAMS Directory for the Tinker Package
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      This directory contains the force field parameter sets distributed
      with the Tinker package, implementing a selection of widely-used
      literature force fields as well as the AMOEBA force field now
      under development in the Ponder lab. We try to exactly reproduce
      the intent of the original authors of our distributed, third-party
      force fields. In all cases the parameter sets have been validated
      against literature reports, results as provided by the original
      developers, or calculations made with the authentic programs. With
      the few exceptions noted below, Tinker calculations can be treated
      as authentic results from the genuine force fields. Please inform
      the Tinker developers of any discrepancies. A brief description of
      each parameter set is provided below:

      amber94    Amber ff94 parameters for proteins and nucleic acids.
                 Note that N- and C-terminal amino acid charges differ
                 slightly from the authentic charge values;; note that
                 N- and C-terminal amino acid charges differ slightly
                 from the authentic charge values

      amber96    Amber ff96 parameters for proteins and nucleic acids.
                 The only changes from Amber ff94 are in the phi/psi
                 torsional parameters

      amber98    Amber ff98 parameters for proteins and nucleic acids.
                 The only changes from Amber ff94 are in the glycosidic
                 torsional parameters

      amber99    Amber ff99 parameters for proteins and nucleic acids.
                 Uses the Cornell, et al (parm94) electrostatic model
                 but changes several geometric values from the above
                 Amber force fields

      amber99sb  Amber ff99sb parameters for proteins and nucleic acids;
                 the only changes from Amber ff99 are to torsional
                 parameters for phi/psi and phi'/psi', the latter being
                 the angles to the beta carbon atom

      amber14sb  Amber ff14sb parameters for proteins as an improvement
                 on ff99sb, combined with OL15 DNA and OL3 RNA parameters
                 for nucleic acids, and TIP3P water parameters; note that
                 N- and C-terminal amino acid charges differ slightly
                 from the authentic charge values

      amber19sb  Amber ff19sb parameters for proteins as an improvement
                 on ff14sb, combined with OL21 DNA and OL3 RNA parameters
                 for nucleic acids, and OPC water parameters; note that
                 N- and C-terminal amino acid charges differ slightly
                 from the authentic charge values

      amoeba     AMOEBA force field for various small organic molecules
                 based on polarizable atomic multipole electrostatics;
                 both 2004 (amoeba04) and 2009 (amoeba09) are provided

      amoebabio  Biopolymer parameters (protein and nucleic acid) for
                 the AMOEBA polarizable atomic multipole force field;
                 the 2009 and 2018 versions are provided; the -HFC23
                 modification of 2018 parameters from the Varma group
                 reworks many parameters involving ion interactions

      amoebail   Ionic liquid parameters for the AMOEBA force field as
                 provided by Andres Cisneros at Univ. Texas at Dallas

      amoebanuc  Nucleic acid parameter for the AMOEBA polarizable atomic
                 multipole force field. The 2017 version is provided

      amoebapro  Protein parameters for the AMOEBA polarizable atomic
                 multipole force field; the original 2004 version and
                 current 2013 version are provided

      basic      A generic parameter file intended for simple and fast
                 geometry optimization of crude structures to avoid
                 steric clashes; the bond, angle and torsion parameters
                 are set to idealized values; the vdw values are loosely
                 based on OPLS, and electrostatics is largely neglected

      charmm19   CHARMM19 parameters for proteins and water; the nucleic
                 acid values are not yet implemented; there are some
                 differences between authentic CHARMM19 and the Tinker
                 version due to replacement of CHARMM impropers by
                 torsions for cases that involve atoms not bonded to
                 the trigonal atom and Tinker's use of all possible
                 torsions across a bond instead of a single torsion
                 per bond

      charmm22   CHARMM22 parameters for proteins, plus heme and lipids;
                 most of the nucleic acid and small model compound values
                 are not yet implemented. The file almost exactly
                 reproduces authentic CHARMM energies; there are small
                 differences are related to Tinker symmetrization of some
                 improper torsions

      charmm27   CHARMM27 parameters for proteins, plus heme and lipids.
                 Identical to CHARMM22, except for addition of a CMAP
                 torsion-torsion phi-psi correction; most nucleic acid and
                 model compound values are not implemented; there are small
                 changes from authentic CHARMM related to symmetrization of
                 some improper torsions, as well as in the CMAP correction

      charmm36m  CHARMM36 parameters for proteins and nucleic acids; these
                 parameters include the CHARMM36m modifications intended
                 to provide a balanced model for folded and disordered
                 protein structures

      dang       Polarizable force field parameters from Liem Dang at
                 Pacific Northwest National Laboratory

      hippo19    Preliminary parameters from 2019 for the HIPPO model
                 covering the monomer molecules in the S101 database;
                 these parameters are very preliminary, subject to
                 revision, and should not be used for production work

      hoch       Simple NMR-NOE force field of Hoch and Stern

      iwater     Parameters for an AMOEBA-like polarizable multipole
                 model for water including only "direct" (non-iterative)
                 polarization

      mm2        Full MM2(1991) parameters including pi-systems; the
                 anomeric and electronegativity correction terms are
                 not implemented

      mm3        Full MM3(2000) parameters including pi-systems. The
                 directional hydrogen bonding and electronegativity
                 bond length correction terms are implemented, but
                 the anomeric and Bohlmann correction terms are not
                 implemented

      mm3pro     Protein-only version of the MM3 parameters; the
                 dielectric constant and some bond stretch and torsion
                 parameters are set to values recommended for high
                 dielectric and/or bulk environments

      mmff94     Full MMFF94 parameters for the Merck Molecular Force
                 Field; validated against the data suite originally 
                 deposited with the Computational Chemistry List (CCL)

      mmff94s    A modified version of the MMFF94 parameters which exhibit
                 greater bias toward planarity at many types of trigonal
                 nitrogan such as amides, ureas, anilines, etc.

      oplsaa08   OPLS-AA parameters from July 2008 with all-atom parameters
                 for proteins, nucleic acids and many general classes of
                 organic molecules

      oplsaa24   OPLS-AA parameters based on results for a series of small
                 organic molecules generated by the LigParGen server, for
                 use as templates to transfer to similar functional groups

      oplsaal    A modified version of the 1997 OPLS-AA with optimized
                 torsional parameters for the protein backbone and side
                 chains as published in 2001

      oplsua97   OPLS-UA containing united-atom parameters from 1997 for
                 proteins and many types of organic molecules; explicit
                 hydrogens on polar atoms and aromatic carbons

      smoothaa   Parameters for use with the Tinker potential energy
                 smoothing methods. Based on the OPLS-AA parameters, but
                 with modifications to vdw and improper torsion terms

      smoothua   Similar to SMOOTHAA, but based on OPLS-UA parameters

      uwater     An AMOEBA-like water model, but having only a single
                 polarizable multipole site centered on the oxygen atom

      water03    The original 2003 AMOEBA water model parameters for a
                 polarizable multipole electrostatics model

      water14    Parameters for a revision of the 2003 AMOEBA water model
                 fit to cluster data and a number of liquid properties
                 using the Force Balance optimization method

      water21    Final HIPPO water parameters including charge flux terms,
                 as published in 2021

      water22    An update of the AMOEBA 2003 water model derived by
                 Chengwen Liu at Univ. of Texas-Austin; tunable parameters
                 are vdw and bond/angle constants; the model provides
                 good agreement with experiment and high-quality QM data
