Usage:
addcharge std [spec atom-spec] [chargeModel version]

Usage:
addcharge nonstd atom-spec net-charge [method am1 | gas ]

Usage:
addcharge [all [spec atom-spec] [chargeModel version] [method am1 | gas ]]

Addcharge is the command-line implementation of Add Charge. It assigns atomic partial charges and Amber/GAFF atom types as the attributes charge and gaffType, respectively. Atomic partial charges are included in saved Mol2 files. The charges and Amber/GAFF atom types are used by other Chimera tools such as Minimize Structure.

Charge assignment requires explicit hydrogens, which can be added beforehand with AddH (or the command addh). Structures often have problems such as truncated sidechains that can lead to non-integral net charges. The Dock Prep tool includes options for fixing such problems prior to hydrogen addition and charge assignment.

• Atoms in standard residues (water, standard amino acids, standard nucleic acids, and a few common variants and capping groups) are assigned charges and types from Amber (details for standard residues).

  The keyword std (or s) indicates assignments should only be made to standard residues. If spec is used, the charge assignment will be limited to the entire model(s) containing the specified atoms.

  The keyword chargeModel indicates Amber force field version (details):

  • ff14SB or 14SB (default)
  • ff02pol.r1 or 02pol.r1 (however, polarizability is not supported by minimize, see note)
  • ff03ua or 03ua - treats amino acid sidechain aliphatic hydrogens as if collapsed onto the corresponding carbons; these “extra” hydrogens will be removed (however, the united-atom approach is not supported by minimize, see note)
  • ff03.r1 or 03.r1
  • ff99SB or 99SB (deprecated)
  • ff99bsc0 or 99bsc0 (deprecated)

• Except for monatomic ions, which are simply assigned their net charges, atoms in nonstandard residues are assigned charges and GAFF types determined by Antechamber, which is included with Chimera (details for nonstandard residues).

  The keyword nonstd (or n) indicates assignments should only be made to nonstandard residues containing the specified atoms. All of these residues must be of the same type (with the same residue name and containing the same types of atoms connected in the same way). The net-charge for that type of residue must also be supplied; it can be zero, or a positive or negative integer. The charge calculation method can be am1-bcc (default, synonym am1) or gasteiger (synonym gas).

• The keyword all (or a, or the absence of arguments) indicates charges should be assigned to both standard and nonstandard residues. If atoms are specified, the charge assignment will be limited to the entire model(s) containing the specified atoms. If nonstandard residues are found, a dialog for specifying their net charges will appear. The chargeModel for standard residues and charge calculation method for nonstandard residues can be specified as described above.

If a nucleic acid chain has a 5' terminal phosphate, the user will be asked whether this group should be deleted; otherwise, its atoms will be assigned charges of zero (the Amber charge set lacks parameters for 5' phosphates).

Unrecognized atom names and non-integral net charges are reported in the Reply Log; such problems should be examined and resolved. Note that chain-terminal nucleotide residues will normally have non-integral charges, but the 5' and 3' charges sum to an integer.

See also: addh, defattr, setattr, minimize, pdb2pqr, Dock Prep, reading charges from files