Z-matrix input

The Z-matrix input provided with DALTON is quite rudimentary, and common options like parameter representations of bond length and angles as well as dummy atoms are not provided. Furthermore, the Z-matrix input is not used in the program, but instead immediately converted to Cartesian coordinates which are then used in the subsequent calculation. Another restriction is that if Z-matrix input is used, one cannot punch ones own basis set, but must instead resort to one of the basis sets provided with the basis set library (i.e. BASIS in first line). Finally, you cannot explicitly specify higher symmetry in input line 4 when using Z-matrix input, you can only request no symmetry ($C_1$) with Nosymmetry or allow DALTON to detect symmetry automatically.

The input format is free, with the restriction that the name of each atom must be given a space of 4 characters, and none of the other input variables needed must be placed in these positions.

The program will use Z-matrix input if there is the word "ZMAT" in the first four position of line 6 in the molecule input. The following NONTYP lines contain the Z-matrix specification for the NONTYP atoms.

A typical Z-matrix input could be:

BASIS
6-31G**
   Test Z-matrix input of ammonia
   6-31G** basis set
Atomtypes=4
ZMAT
N   1 7.0
H1  2 1 1.0116 1.0
H2  3 1 1.0116 2 106.7 1.0
H3  4 1 1.0116 2 106.7 3 106.7 1 1.0

The five first lines should be familiar by now, and will be discussed no further here. The special 6'th line tells that this is Z-matrix input. The Z-matrix input starts on line 7, and on this first Z-matrix line only the atom name, a running number and the charge of the atom is given. The running number is only for ease of reference to a given atom, and is actually not used within the program, where any reference to an atom, is the number of the atom consecutively in the input list.

The second Z-matrix line consists of the atom name, a running number, the number of the atom to which this atom is bonded with a given bond length in Ångströms, and then finally the charge of this atom.

The third Z-matrix line is identical to the second, except that an extra atom number, to which the two first atoms on this line is bonded to with a given bond angle in degrees.

On the fourth Z-matrix line yet another atom has been added, and the position of this atom relative to the three previous ones on this line is dependent upon on an extra number inserted just before the nuclear charge of this atom. If the next to last number is a 0, the position of this atom is given by the dihedral angle (A1,A2,A3,A4) in degrees, where Ai denotes atom i. If, on the other hand, this next to last number is $\pm 1$, the position of the fourth atom is given with respect to two angles, namely (A1,A2,A3) and (A2,A3,A4). The sign is to be $+ 1$ if the triple product $\overrightarrow{\left(A_{2}A_{1}\right)}\cdot\left[\overrightarrow{\left(A_{2}A_{3}\right)}\times\overrightarrow{\left(A_{2}A_{4}\right)}\right]$ is positive.