The relativity Section of the Jaguar Input File

In this section you can make settings for the use of relativistic Hamiltonians, such as the ZORA Hamiltonian. These settings control details of the Hamiltonian and approximations to it. Currently the scalar ZORA and the spin-orbit ZORA Hamiltonians are available.

For ZORA, you can choose to use the nuclear potential only in the ZORA integrals, or the nuclear and electronic Coulomb (Hartree) potentials. Using the latter is recommended, as it includes the bulk of the electronic screening of the nucleus in the relativistic integrals. The electronic Coulomb potential is evaluated with the atomic initial guesses, and is not changed during the calculations.

You can also choose to evaluate only the one-center relativistic contributions to the ZORA Hamiltonian. This is an approximation to the full ZORA method, but is a good approximation as the relativistic effects are well localized on the atoms. Its advantages are that it eliminates the gauge dependence of the ZORA method, and it allows geometry optimizations and frequency calculations to be performed at no extra cost.

Table 1. Keywords for the ZORA Hamiltonian
Keyword	Value	Meaning
nucmodel	`point`	Model the nuclear charge distribution as a point charge, for which the potential is −Z/r. This is the default.
	`gaussian`	Model the nuclear charge distribution as a Gaussian charge distribution Z (η/π^1/2)³ exp(−η²r²), for which the potential is −Z erf(ηr)/r. The value of η is determined from a standard expression for the nuclear RMS radius [275].
potential	`local`	Evaluate ZORA integrals as one-center integrals, using one-center (atomic) nuclear and electronic Coulomb (Hartree) potentials. This is an approximation, but it removes the gauge dependence of the ZORA method. This is the default.
	`global`	Evaluate ZORA integrals as multi-center integrals, using the global (molecular) nuclear and electronic Coulomb potentials.
	`local_nucl`	Evaluate ZORA integrals as one-center integrals, using only the one-center (atomic) nuclear potential.
	`global_nucl`	Evaluate ZORA integrals as multi-center integrals, using the sum of nuclear potentials from all centers.
relatom	element-list	Space-separated list of elements (symbols) for which ZORA relativistic corrections should be applied. This keyword should be used in conjunction with the `local` or `local_nucl` values of the potential keyword. By default, atoms with Z < 18 are treated nonrelativistically, so you must use this keyword to apply ZORA relativistic corrections to these atoms.