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NMR, IR, and Raman

Source access and public downloads

Repository paths identify files in the licensed engine source; they are not public downloads. For freely downloadable .oqp inputs and results, see Worked Examples.

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:

  • examples/HESS/H2O_RHF-DFT_ANA_HESS.oqp
  • examples/HESS/H2O_RHF-DFT_NUM_HESS.oqp
  • examples/HESS/H2Oplus_UHF_ANA_HESS_IR_RAMAN.oqp
  • examples/HESS/H2Oplus_ROHF_ANA_HESS_IR_RAMAN.oqp

Scientific references

Vibrational and magnetic properties.