A benchmark study of molecular structure by experimentaland theoretical methods: Equilibrium structure of uracil from gas-phase electron diffraction data and coupled-cluster calculationsстатья
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Дата последнего поиска статьи во внешних источниках: 24 декабря 2013 г.
Аннотация:The equilibrium structure of uracil, one of the nucleobases, which build nucleic acids, has been determined
for the first time by the gas-phase electron diffraction (GED) method. The necessary rovibrational
corrections to the experimental internuclear distances have been calculated with quadratic and cubic
force constants in the MP2(all)/cc-pVTZ approximation. For the first time, the equilibrium structure
has been optimized by the very time-consuming coupled-cluster method with single and double excitations
and perturbative treatment of connected triples using the correlation-consistent polarized
weighted core-valence triple-zeta basis set with all electrons being correlated (CCSD(T)(all)/cc-pwCVTZ).
The optimized structural parameters have been corrected for the diffuse-function effects and extrapolated
to the higher basis set (cc-pwCVQZ) using results of MP2 computations (named as best ab initio
structure). The GED equilibrium structure remarkably agrees with the best ab initio one as well as with
that one derived from microwave (MW) rotational constants by Puzzarini and Barone. Thus, it has been
revealed that the precise experiment and coupled-cluster calculations yield the same results when accurate
vibrational corrections (including anharmonic ones) are considered in the experimental structural
analysis. Moreover, it has been shown that the equilibrium structure derived from the GED data, being
in general of one order less accurate than that determined from the MW rotational constants, is still reliable
and accurate.