17.1.3.1 Static Properties of Internal Coordinates

All the internal coordinate tables (BOND, ANGLE, TORSION, and IMPROPER) have the same set of properties. The syntax for these properties is as follows:

                  {GEOMETRY}
     property ::= { ENERGY }
                  { NUMBER }

The GEOMETRY property returns the geometry of the internal coordinate. For example the BOND GEOMETRY is the bond length; the TORSION GEOMETRY is the torsion angle. The ENERGY property returns the energy of the the internal coordinate. For example, IMPROPER ENERGY returns the energy of the improper torsion angles. The NUMBER property returns the sequential position of the internal coordinate in the list contained in the PSF. For example, the numbers of the sulfur-sulfur bonds in a cysteine bridge will be very large, because they are added last. The NUMBER property is useful in figuring out error messages from the energy routines as the numbers the energy routines output correspond to the numbers returned by this property.