Accurate molecular structure and spectroscopic properties of nucleobases: a combined computational–microwave investigation of 2-thiouracil as a case study

Abstract

The computational composite scheme purposely set up for accurately describing the electronic structure and spectroscopic properties of small biomolecules has been applied to the first study of the rotational spectrum of 2-thiouracil. The experimental investigation was made possible thanks to the combination of the laser ablation technique with Fourier transform microwave spectrometers. The joint experimental-computational study allowed us to determine the accurate molecular structure and spectroscopic properties of the title molecule, but more importantly, it demonstrates a reliable approach for the accurate investigation of isolated small biomolecules.

Characterizing the dark state in thymine and uracil by double resonant spectroscopy and quantum computation

“…Comparison of the results of PT2 with both 1D-PT2 and 1D-scan indicate a relatively small coupling between NH stretching modes and other degrees of freedom. In addition, these calculations which accounted for fulldimensional anharmonicity provided frequencies in a very good agreement with the experiment, confirming that this is the diketo tautomer as seen in previous experiments [49][50][51][52][53][54] . The frequencies appear as blue stick spectra in Figures 3 and 4.…”

What are the spectroscopic properties of HFC-32? Answers from DFT

“…Thanks to the huge progresses made in computer hardware resources and the development of efficient algorithms, in the last years coupled cluster (CC) theory with singles, doubles excitations and a perturbative estimate of connected triples, [1,2] CCSD(T), coupled to large basis sets or complete basis set extrapolation, has become the gold standard for the accurate prediction of thermochemical and spectroscopic properties of small molecules, containing up to a 10th of atoms (e.g., see Refs. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and references therein). Nevertheless, due to the unfavorable scaling of CCSD(T) with system size (N 6 -N 7 , N being the number of basis functions), the method cannot be routinely applied to medium and large systems which are of relevance in biochemistry, supramolecular chemistry, solid state chemistry, and material science.…”

Validating additive correction schemes against gradient‐based extrapolations

“…Perhaps this is why the use of empirical, additive correction schemes to obtain structural parameters, and even properties of molecules has been recently gaining traction. The application of such correction schemes to geometries of increasingly larger systems is becoming more common . The approach has been also applied to harmonic frequencies, as well as dipole moments .…”

“…In short, for geometries, this approach consists of optimizing the structures at each level of theory in the “recipe” individually, and then combining the structural parameters (radii, angles, dihedrals) directly to obtain a “best” composite estimate. In analogy with the above energy scheme, an equivalent geometry‐based correction scheme would be where r x corresponds to an extrapolated value of the parameter (radius), either by optimizing the extrapolated gradient or more commonly by extrapolating the radii directly . The angles, dihedrals, as well as harmonic frequencies can be obtained analogously.…”