@article{Boese2015, author = {Boese, Adrian Daniel}, title = {Density Functional Theory and Hydrogen Bonds: Are We There Yet?}, series = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, volume = {16}, journal = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, number = {5}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1439-4235}, doi = {10.1002/cphc.201402786}, pages = {978 -- 985}, year = {2015}, abstract = {Density functional theory (DFT) has become more successful at introducing dispersion interactions, and can be thus applied to a wide range of systems. Amongst these are systems that contain hydrogen bonds, which are extremely important for the biological regime. Here, the description of hydrogen-bonded interactions by DFT with and without dispersion corrections is investigated. For small complexes, for which electrostatics are the determining factor in the intermolecular interactions, the inclusion of dispersion with most functionals yields large errors. Only for larger systems, in which van der Waals interactions are more important, do dispersion corrections improve the performance of DFT for hydrogen-bonded systems. None of the studied functionals, including double hybrid functionals (with the exception of DSD-PBEP86 without dispersion corrections), are more accurate than MP2 for the investigated species.}, language = {en} } @article{Boese2015, author = {Boese, Adrian Daniel}, title = {Basis set limit coupled-cluster studies of hydrogen-bonded systems}, series = {Molecular physics}, volume = {113}, journal = {Molecular physics}, number = {13-14}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0026-8976}, doi = {10.1080/00268976.2014.1001806}, pages = {1618 -- 1629}, year = {2015}, abstract = {As hydrogen-bonded systems are of utmost importance in especially biological and chemical systems, a new set of highly accurate reference dissociation energies, denoted HB49, is devised. For the molecules in this set, the basis set convergence of post-Hartree-Fock methods, including F12 methods, is investigated. Using combined Moller-Plesset perturbation theory (MP2) and CCSD(T) approaches for energies and MP2 and QCISD(T) for gradients, we achieve CCSD(T) accuracy, which has been determined before to yield an accuracy of 0.2 kJ/mol for a subset of HB49. Both conventional extrapolation techniques and F12 techniques are competitive with each other. By using MP2+Delta CCSD(T), a rather fast basis set convergence is obtained when both basis sets are carefully chosen.}, language = {en} } @article{BoeseBoese2015, author = {Boese, Adrian Daniel and Boese, Roland}, title = {Tetrahydrothiophene and Tetrahydrofuran, Computational and X-ray Studies in the Crystalline Phase}, series = {Crystal growth \& design : integrating the fields of crystal engineering and crystal growth for the synthesis and applications of new materials}, volume = {15}, journal = {Crystal growth \& design : integrating the fields of crystal engineering and crystal growth for the synthesis and applications of new materials}, number = {3}, publisher = {American Chemical Society}, address = {Washington}, issn = {1528-7483}, doi = {10.1021/cg501228w}, pages = {1073 -- 1081}, year = {2015}, abstract = {Calculations at various levels of theory with different methods and respective evaluations confirm that the twist conformation (C-2) is preferred for tetrahydrothiophene (THT) in the gas phase. In the crystalline phase, achieved by a laser assisted crystallization device, THT has C-1 symmetry (slightly distorted C-2 symmetry) in the chiral space group P2(1)2(1)2(1). This is obviously a packing effect caused by the nonsymmetrical arrangement of neighboring molecules. The distortion from C-2 symmetry costs very little energy as confirmed by computational methods in the gas phase. Only one enantiomer of the chiral THT is found in the cell which requires spontaneous crystallization, which results in a racemic mixture of crystals, or a racemization occurs prior to/during nucleation or in the embryonic state. The racemization happens by a mechanism that can be described as a partial pseudo rotation within a five-membered mono-heterocycle with a C-2-C-S-C-2' transition (C-2 and C-2' are enantiomers) maintaining the heteroatom residing within the symmetry elements. While THT has the molecular symmetry of the gas phase almost also in the crystalline phase, THF has an envelope conformation (CS). This was also established by calculations at various levels of theory which agrees well with the previously experimentally found conformation by electron diffraction. However, in the X-ray crystal structure, previously determined by Luger \& Buschmann, THF has C-2 symmetry in the centrosymmetric space group C2/c with the oxygen atom situated on the crystallographic C-2 polar axis, requesting a racemic crystal for the twisted conformers of the enantiomers. No solid-state phase transitions were detected within the experimental ranges for THT and THF. Following the stabilization by molecular clustering, and ending at the crystal lattice, we stepwise increased the number of molecules by calculation of the respective monomers, dimers, trimers, and tetramers for THF and THT. The starting point was taken from the arrangements as found in the respective crystal structures. Both conformational enantiomers are equal in energy. In such cases, a crystal may contain either a racemate of conformers or one of the conformational enantiomers only. The first case is observed in THF, the latter one in THT. It is quite likely that the selection of one enantiomeric conformer of THT from an equilibrium of conformers at the early stage of nucleation (embryonic stage) is responsible for the spontaneous crystallization. In order to check if THF could form a polymorph with the molecular packing of THT and vice versa, we first calculated THF and THT in their respective crystal lattices as determined by X-ray diffraction. Exchanging the compounds in the THT and THF crystal lattices (i.e., replacing O against S and vice versa) results in significantly worse lattice energies indicating that such a polymorph is not a probable option.}, language = {en} } @article{CodorniuHernandezHallBoeseetal.2015, author = {Codorniu-Hernandez, Edelsys and Hall, Kyle Wm. and Boese, Adrian Daniel and Ziemianowicz, Daniel and Carpendale, Sheelagh and Kusalik, Peter G.}, title = {Mechanism of O(P-3) Formation from a Hydroxyl Radical Pair in Aqueous Solution}, series = {Journal of chemical theory and computation}, volume = {11}, journal = {Journal of chemical theory and computation}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {1549-9618}, doi = {10.1021/acs.jctc.5b00783}, pages = {4740 -- 4748}, year = {2015}, abstract = {The reaction mechanism for the rapid formation of a triplet oxygen atom, O(P-3), from a pair of triplet-state hydroxyl radicals in liquid water is explored utilizing extensive Car-Parrinello MD simulations and advanced visualization techniques. The local solvation structures, the evolution of atomic charges, atomic separations, spin densities, electron localization functions, and frontier molecular orbitals, as well as free energy profiles, evidence that the reaction proceeds through a hybrid (hydrogen atom transfer and electron proton transfer) and hemibond-assisted reaction mechanism. A benchmarking study utilizing high-level ab initio calculations to examine the interactions of a hydroxyl radical pair in the gas phase and the influence of a hemibonded water is also provided. The results presented here should serve as a foundation for further experimental and theoretical studies aimed at better understanding the role and potential applications of the triplet oxygen atom as a potent reactive oxygen species.}, language = {en} }