NMR, IR, and Raman¶

NMR Shielding¶

Request NMR shielding with the nmr modifier.

.oqp:

hf/sto-3g nmr(gauge=cgo)
geom="h2o.xyz"

Python:

from oqp.openqp import OpenQP

job = OpenQP("h2o_nmr", silent=1)
job.molecule(geometry="water", charge=0, multiplicity=1)
job.theory.hf(basis="sto-3g")
job.workflow.nmr(gauge="cgo")

mol = job.run()

Canonical .oqp input:

rhf/sto-3g properties(scf_prop=nmr)
geom="molecule.xyz"

Runnable .oqp: examples/NMR/H2O_RHF-NMR.oqp.

nmr_gauge accepts:

Value	Meaning
`cgo`	Common-gauge-origin shielding.
`giao`	Gauge-including atomic orbital shielding where supported.

ACID maps come from the same call, but they need the GIAO response, so switch the gauge as well as enabling them -- nmr(gauge=giao,acid=true) rather than the gauge=cgo used above, which the input checker refuses with acid. See ACID Current-Density Maps.

job.workflow.nmr(...) requires an HF/DFT reference-SCF theory. CGO NMR is limited to closed-shell RHF; use gauge="giao" for open-shell UHF/ROHF references. The helper also blocks range-separated and meta-GGA functionals for NMR because those paths are not implemented.

IR and Raman¶

IR and Raman intensities are produced from supported Hessian/frequency workflows. See Hessian and Frequencies for the main Hessian workflow page.

With the analytical ground-state Hessian (RHF/RKS, UHF/UKS, ROHF/ROKS), the intensities are analytic and need no extra calculations:

IR. Comes from the nuclear derivatives of the dipole moment, built from the relaxed density derivatives the Hessian already computes.
Raman. Comes from the nuclear derivatives of the static polarizability.
It needs three extra CPHF right-hand sides plus a fixed number of derivative-integral passes, independent of the number of atoms.
For Kohn-Sham, the exchange-correlation terms are central differences along the relaxed orbital path; no SCF or CPHF is re-solved.
Effective core potentials. These cases are included.
Numerical Hessian. Intensities still come from finite differences: 6N displaced SCF + CPHF calculations.
Log. The log states which backend produced the intensities, and the .hess.json sidecar records it in vibrational_intensity_metadata.

.oqp:

dft/bhhlyp/6-31g* hess(S0,type=analytical) ir raman
geom="h2o.xyz"

Python:

from oqp.openqp import OpenQP

job = OpenQP("h2o_freq", silent=1)
job.molecule(geometry="water", charge=0, multiplicity=1)
job.theory.dft(functional="bhhlyp", basis="6-31g*")
job.workflow.hessian(type="analytical", state=0)

mol = job.run()

Canonical .oqp input:

rks/bhhlyp/6-31g* hess(S0,type=analytical)
geom="molecule.xyz"

Runnable .oqp inputs:

Scientific references¶

Vibrational and magnetic properties.