Z-matrix input

 

The Z-matrix input  provided with DALTON is very rudimentary, and common options like parameter representations of bond length and angles as well as dummy atoms are currently 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 basis sets provided with the basis set library.

The input format is free, with, once more, the restriction that the name of each atom must be of 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 are any characters in the first 4 positions of line 6 in the molecule input, and it is important that these positions are kept blank if a Cartesian coordinate input is used.

A typical Z-matrix input could be:

BASIS
6-31G(d,p)
Test input of ammonia
6-31G(d,p) basis set
    4
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 Z-matrix input starts on line 6, and on the first 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 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, and then finally the charge of this atom.

The third 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.

On the fourth 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), where Ai denotes atom i. If, on the other hand, this next to last number is , 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 is positive.