The cdft Section of the Jaguar Input File

The cdft section specifies the constraints used to constrain charge density or spin density to certain atoms in a DFT calculation. The syntax of a constraint involves specifying the net charge or spin density on a group of atoms, and a list of atom ranges with weights, in the format

density-value
weight1 first-atom1 last-atom1
weight2 first-atom2 last-atom2
...

Each group of atoms is specified by a lower and an upper index, where the index is the atom index in the zmat section. All atoms in the range (inclusive) are included in the constraint region, and the weight specifies the relative amount of charge or spin density to be localized in the group. For example, in a calculation with icdft=1 for charge density, the section

&cdft
-1.0
1.0 1 3
2.0 4 5
&

specifies that a net charge of −1 should be distributed over atoms 1 through 5, with relative weights of 1.0 on atoms 1 through 3, and 2.0 on atoms 4 through 5. The total weight summed over all atoms is 7.0, so atoms 1 through 3 have a net charge of −1/7, and atoms 4 and 5 have a net charge of −2/7.

Atom groups can be overlapping. You can add multiple blocks to this section that define a value and a set of atom groups to distribute the value over.

Any atoms that are not in a constraint group will end up with the leftover charge or spin density, i.e. the difference between the charge on the entire structure and the sum of the net charges in each group, or the difference between 2S (twice the spin) and the sum of the spin density values in each group.

Note that the value given for the spin density here is the difference between the integrated alpha electron density and the integrated beta electron density, which is twice the spin (M_S) for the group.