Hypertext Dalton 2.0 manual - Theoretical Chemistry, KTH

CHAPTER 25.
HF, SOPPA, AND MCSCF MOLECULAR PROPERTIES, ABACUS240
.SHIELD Invokes the calculation of nuclear shielding constants. By default this is done using
London orbitals in order to ensure fast basis set convergence as shown in Ref. [54, 55].
The use of London orbitals can be disabled by the keyword .NOLOND.
Furthermore, the natural connection (Ref. [64, 82]) is the default in order to ensure
numerically stable results as well as physically interpretable results for the paramagnetic
and diamagnetic terms. The natural connection can be turned off by the
keyword .NODIFC in which case the symmetric connection is used instead.
The gauge origin is chosen to be the center of mass of the molecule. This origin can
be changed by the two keywords .GAUGEO and .NOCMC . This choice of gauge origin
will not affect the final shieldings if London orbitals are used, only the size of the diaand
paramagnetic contributions.
Combined with the keyword .SOPPA or .SOPPA(CCSD) it invokes a SOPPA or SOPPA(CCSD)
calculation of the Nuclear Magnetic Shieldings (Ref. [58, 59, 60]). London orbitals are
automatically disabled in SOPPA or SOPPA(CCSD) calculations. Gauge origin independent
SOPPA or SOPPA(CCSD) calculations of Nuclear Magnetic Shieldings can
be carried out with the CTOCD-DZ method (see Refs. [58, 59, 60]) using the keyword
.CTOCD.
In combination with the keyword .CTOCD this invokes a calculation of the Nuclear
Magnetic Shieldings without the use of London orbitals but with both the CTOCD-
DZ method (Ref. [58, 59, 60]) and with the common origin method. For the CTOCD-
DZ method the Nuclear Magnetic Shieldings are given in the output file for both the
origin at the center of mass and at the respective atoms. Changing the default value
of the gauge origin could give wrong results!
.SOPPA Indicates that the requested molecular properties be calculated using the secondorder
polarization-propagator approximation [51]. This requires that the MP2 energy
and wave function have been calculated. London orbitals can not be used together
with the SOPPA approximation.
.SOPPA(CCSD) Indicates that the requested molecular properties be calculated using the
Second-Order Polarization-Propagator Approximation with Coupled Cluster Singles
and Doubles Amplitudes [53, 63, 52, 60]. This requires that the CCSD energy and
wave function have been calculated. London orbitals can not be used together with
the SOPPA(CCSD) approximation.
.SPIN-R Invokes the calculation of spin-rotation constants as described in Ref. [74]. By
default this is done using London orbitals and the natural connection. The use of
London orbitals can be turned off by the keyword .NOLOND.