High-throughput approaches for producing
approximate vibrational
spectral data for molecules of astrochemistry interest rely on harmonic
frequency calculations using computational quantum chemistry. However,
model chemistry recommendations (i.e., a level of theory and basis
set pair) for these calculations are not yet available and, thus,
thorough benchmarking against comprehensive benchmark databases is
needed. Here, we present a new database for vibrational frequency
calculations (VIBFREQ1295) storing 1295 experimental fundamental frequencies
and CCSD(T)(F12*)/cc-pVDZ-F12 ab initio harmonic
frequencies from 141 molecules. VIBFREQ1295’s experimental
data was complied through a comprehensive review of contemporary experimental
data, while the ab initio data was computed here.
The chemical space spanned by the molecules chosen is considered in-depth
and is shown to have good representation of common organic functional
groups and vibrational modes. Scaling factors are routinely used to
approximate the effect of anharmonicity and convert computed harmonic
frequencies to predicted fundamental frequencies. With our experimental
and high-level ab initio data, we find that a single
global uniform scaling factor of 0.9617(3) results in median differences
of 15.9(5) cm–1. A far superior performance with
a median difference of 7.5(5) cm–1 can be obtained,
however, by using separate scaling factors (SFs) for three regions:
frequencies less than 1000 cm–1 (SF = 0.987(1)),
between 1000 and 2000 cm–1 (SF = 0.9727(6)),
and above 2000 cm–1 (SF = 0.9564(4)). This
sets a lower bound for the performance that could be reliably obtained
using scaling of harmonic frequency calculations to predict experimental
fundamental frequencies. VIBFREQ1295’s most important purpose
is to provide a robust database for benchmarking the performance of
any vibrational frequency calculations. VIBFREQ1295 data could also
be used to train machine-learning models for the prediction of vibrational
spectra and as a reference and data starting point for more detailed
spectroscopic modeling of particular molecules. The database can be
found as part of the Supporting Information for this paper or in the
Harvard DataVerse at .
