Nuclear shielding constants

The calculation of nuclear shieldings are invoked by the keyword .SHIELD in the **PROPERTIES input module. Thus a complete input file for the calculation of nuclear shieldings will be:

**DALTON INPUT
.RUN PROPERTIES
**WAVE FUNCTIONS
.HF
**PROPERTIES
.SHIELD
**END OF DALTON INPUT

This will invoke the calculation of nuclear shieldings using London Atomic Orbitals to ensure fast basis set convergence and gauge origin independent results. The natural connection [64] is used in order to get numerically accurate results. By default the center of mass is chosen as gauge origin.

For a SOPPA or SOPPA(CCSD) calculation of nuclear shieldings the additional keywords .SOPPA or .SOPPA(CCSD) have to be specified in the **PROPERTIES input module. For SOPPA an MP2 calculation has to be requested by the keyword .MP2 in the **WAVE FUNCTIONS input module, whereas for SOPPA(CCSD) a CCSD calculation has to be requested by the keyword .CC in the **WAVE FUNCTIONS input module with the *CC INPUT option .SOPPA(CCSD). This will also automatically disable the use of London orbitals.

For a CTOCD-DZ calculation of nuclear shieldings the additional keyword .CTOCD has to be specified in the **PROPERTIES input module. This will automatically disable the use of London orbitals. .SOPPA / .SOPPA and .CTOCD could be used together to get gauge origin independent SOPPA / SOPPA(CCSD) nuclear shieldings using the CTOCD-DZ formalism. Information about suitable basis set for CTOCD-DZ calculations can be found in the section 10.9.1.

A basis set well suited for the calculation of nuclear shieldings (and indirect nuclear spin-spin coupling constants) is the TZ basis set of Ahlrichs and coworkers [71,72] with two polarization functions [73]. This basis set is available from the basis set library as TZ2P.

Notice that a general print level of 2 or higher is needed in order to get the individual contributions (relaxation, one- and two-electron expectation values and so on) to the total nuclear shieldings.

If more close control of the different parts of the calculation of the nuclear shieldings is wanted we refer the reader to the section describing the options available. For the calculation of nuclear shieldings, these are the same as listed above for magnetizability calculations.