# fragment

Specify a fragment of a molecule/system by providing the indices of atoms, and optionally, the charge and spin. This command can appear in the global context.

### Options

atoms

Specify the indices of atoms belonging to this fragment. The atoms are indexed from 1

• The type is [int]
• There is no default value.
• The value must be positive
charge

Total charge on this fragment. Note that non-integer values are possible as well.

• The type is real
• There is no default value.
multiplicity

Spin multiplicity - only valid for integer-electron calculations. For non-integer-electron number, or for higher multiplcities, use the spin option.

By default entos selects the lowest available spin multiplicity.

• The type is string
• There is no default value.
• The value must be one of:
• singlet - S = 0
• doublet - S = 1/2
• triplet - S = 1
• quartet - S = 3/2
• quintet - S = 2
• sextet - S = 5/2
spin

For spin-unrestricted calculations, the spin $$2S$$.

Notice that the value of this option need not be an integer. See the documentation on spin_z for an explanation.

By default entos selects the lowest available spin multiplicity.

• The type is real
• There is no default value.
• The value must be nonnegative