Q-Chem 4.3 User’s Manual

3.4 Cartesian Coordinates

Q-Chem can accept a list of $N$ atoms and their $3N$ Cartesian coordinates. The atoms can be entered either as atomic numbers or atomic symbols where each line corresponds to a single atom. The Q-Chem format for declaring a molecular geometry using Cartesian coordinates (in Angstroms) is:

atom  x-coordinate  y-coordinate  z-coordinate

Note: The geometry can by specified in bohr; to do so, set the INPUT_BOHR $rem variable to TRUE.

3.4.1 Examples

Example 3.6  Atomic number Cartesian coordinate input for H$_{2}$O.

   0 1
   8   0.000000   0.000000  -0.212195
   1   1.370265   0.000000   0.848778
   1  -1.370265   0.000000   0.848778

Example 3.7  Atomic symbol Cartesian coordinate input for H$_{2}$O.

   0 1
   O   0.000000   0.000000  -0.212195
   H   1.370265   0.000000   0.848778
   H  -1.370265   0.000000   0.848778

Note: (1) Atoms can be declared by either atomic number or symbol.
(2) Coordinates can be entered either as variables/parameters or real numbers.
(3) Variables/parameters can be declared in any order.
(4) A single blank line separates parameters from the atom declaration.

Once all the molecular Cartesian coordinates have been entered, terminate the molecular coordinate input with the $end keyword.