If no unit is provided the values are assumed to represent distances in either bohr (default) or ångstrom if the ANGSTROM directive has been used. Individual parameters may be given units: A for Angstrom, B for bohr, D for degrees or R for radians. Angles should always have a unit.
VARIABLES name value <unit> name value <unit> . . END CONSTANTS name value <unit> name value <unit> . . ENDThe use of variables and constants will be much clearer if you look at a few example datasets, either those given in this chapter, or those in the chapter on geometry optimisations.
There are two main conventions for defining the signs of dihedral angles.
This keyword has been included to allow the possibility of a change of
definition in the future. At present the definition in CADPAC6 is the same
as that in CADPAC5. Thus the default is 'OLD'. This may be changed in future
editions. For a description of the way dihedral angles are defined see
the definitions of internal coordinates given later in this chapter.
Note that the dihedral angles are not printed by default. They can be printed using the command
This keyword indicates that a standard basis set is to be used in the
calculation. The restrictions are that the basis must be one of the very
standard generic types, that the same level of basis set must be used for
every atom in the system, that extra basis functions cannot be added to
modify the library definitions, and that one cannot use this keyword when
doing basis set superposition corrections via the ghost atom technique
(because the program needs to know the true atomic number in order to find
the right basis set). A more flexible, but more complicated, basis set
specification without these restrictions is available if the LIBRARY
directive is used atom-by-atom. A full list of the basis sets available
is given later when the basis set library is described.