12.3.1 Torsion Angle Maps

The torsion angle maps are simple formatted files containing a set of record giving the energy for each possible value of omega, phi, and psi. The format of the file is as follows:

     title
     count                           (I5)
     omega,phi,psi,etrans,ecis       (3F10.0,2F15.0)

where the count is the number of entries in the file. The omega, phi, and psi torsion angles are in degrees, and the energies, etrans and ecis, are in kcal/mol. Torsion angles are selected using the minimum of etrans and ecis.

A number of standard maps are available in CGDATA:. The files are named as EMAPresnn.OMP where res is one of ALA, GLY, or PRO; and nn is one of 30, 15, 10, 5, or MN. The numeric values are used for files which contain uniform grids over the torsion angles. MN stands for a minimal map which has met with only limited utility in our experience (see the Biopolymers paper for details). When using the MN files, be sure to specify the EMAX variables (see Global Options for Conformational Search) all to zero. The energy values in the ALA and GLY maps are computed for alanine and glycine dipeptides, and consist of just the van der Waals energy for those dipeptides. The trans value (etrans) is computed for the second peptide being trans; the cis value (ecis) is computer for the second peptide being cis. In the case of the proline maps, the energy in the file is the sum of the van der Waals energy and the internal energy of the ring as taken from the proline constructor file, see Proline Constructors.

The makefile in $CGP/emap can be used to generate these files. See Emap, for more information. The files are read by the subroutine, RDEMAP.