Next: The main input file Up: Description of the molecular Previous: Dihedral angles

## Optional features of the force field

Description of the optional features of the force field begins with the line defining the type of additional potential features. These are:

- `tors1`

  describes torsion angles in terms of MM3 potential:

  | (8)

  The first line of this section contains the number of torsions of this type followed by lines in which fields 1)-4) define atoms and fields 5)-7) constants and in for each torsion angle of this type.

- `tors5`

  describes torsion angles given by the Ryckaert-Bellemans potential:

  | (9)

  The first line of this section contains the number of torsions of this type followed by lines in which fields 1)-4) define atoms and fields 5)-9) constants in for each torsion angle of this type.

- `improper`

  improper dihedral potential:

  | (10)

  field 5) is the equilibrium angle in degrees and 6) is the force constant

- `special`

  introduces a list, over-reading Lennard-Jones parameters for 1-4 interactions for the specified atoms. This list consists of the following:

  the first line - number of atoms in the list;

  other lines: the first field defines atom, the second is sigma (Å) and the third parameter is epsilon in .

  Scaling parameter for 1-4 LJ interactions, eventually specified by `slj14` keyword (see below), is applied to these modified LJ parameters also.

- `no_14`

  This parameter tells that all 1-4 pairs must be excluded from the intramolecular Lennard-Jones and electrostatic interactions

- `noi15`

  This parameter tells that all intramolecular electrostatic and LJ interactions are switched off

- `sel14 <factor>`

  Scale 1-4 electrostatic interactions by this factor

- `slj14 <factor>`

  Scale 1-4 Lennard-Jones interactions by this factor

- `fSPC`

  This parameter is exclusively for the flexible SPC model. It tells to the program to compute water intramolecular potential according to the paper by Toukan and Rahman, Phys. Rev. B, 31(2) 2643 (1985)

Examples of `.mmol` files are included into `moldb` directory. For big molecules, procedure of writing `.mmol` files may be somewhat automatized by the utility `makemol`.

Next: The main input file Up: Description of the molecular Previous: Dihedral angles