Abstract
Density functional theory (DFT) is a widely used methodology for the computation of molecular and electronic structure, and we confirm that B3LYP and the high-level ab initio G3B3 method are in excellent agreement for the lowest-energy isomers of the 16 glucose epimers. Density-functional tight-binding (DFTB) is an approximate version of DFT with typically comparable accuracy that is 2 to 3 orders of magnitude faster, therefore generally very suitable for processing large numbers of complex structures. Conformational isomerism in sugars is well known to give rise to a large number of isomer structures. On the basis of a comprehensive study of glucose epimers in vacuo and aqueous solution, we found that the performance of DFTB is on par to B3LYP in terms of geometrical parameters excluding hydrogen bonds and isomer energies. However, DFTB underestimates both hydrogen bonding interactions as well as torsional barriers associated with rotations of the hydroxy groups, resulting in a counterintuitive overemphasis of hydrogen bonding in both gas phase as well as in water. Although the associated root mean squared deviation from B3LYP within epimer isomer groups is only on the order of 1 kcal/mol, this deviation affects the correct assignment of major isomer ordering, which span less than 10 kcal/mol. Both second- as well as third-order DFTB methods are exhibiting similar deviations from B3LYP. Even after the inclusion of empirical dispersion corrections in vacuum, these deviations remain for a large majority of isomer energies and geometries when compared to dispersion-corrected B3LYP.
Original language | English |
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Pages (from-to) | 16899-16915 |
Number of pages | 17 |
Journal | ACS Omega |
Volume | 3 |
Issue number | 12 |
DOIs | |
State | Published - Dec 7 2018 |
Funding
K.H.L. was in part supported by a Master Course fellowship from MEXT, Japan, and by an Energy Science and Engineering Fellowship by the Bredesen Center for Interdisciplinary Research and Graduate Education at the University of Tennessee, Knoxville. Fruitful discussions with Quan Van Vuong are acknowledged. U.S. acknowledges support by the Mund-Lagowski Department of Chemistry and Biochemistry and Bradley University. S.I. acknowledges support by the Laboratory Directed Research and Development (LDRD) Program of Oak Ridge National Laboratory. ORNL is managed by UT-Battelle, LLC, for DOE under contract DE-AC05-00OR22725. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the U.S. DOE Office of Science under Contract DE-AC02-05CH11231.