Through-hydrogen-bond scalar couplings are attractive NMR observables because they connect high-precision spectroscopy with local hydrogen-bond structure. It is less clear whether they can also report hydrogen-bond covalency in amorphous ice and other frozen or heterogeneous aqueous environments. Here, we combine ab initio molecular dynamics configurations of water, density functional response calculations of indirect nuclear spin–spin couplings, and absolutely localized molecular orbital (ALMO) energy decomposition analysis. Benchmark calculations against SOPPA(CCSD) water-dimer references validate BLYP/pcJ-1 for the through-hydrogen-bond 1h J O–H coupling. The coupling is dominated by the Fermi contact term and therefore follows an approximately exponential distance dependence, but ensemble and vibrational averaging prevent a transferable one-dimensional distance ruler. Extending earlier NMR/ALMO work on liquid water, 1h J O–H correlates with ALMO charge-transfer stabilization and charge-transfer amount. Thus, 1h J O–H is an experimentally accessible, covalency-sensitive fingerprint of hydrogen bonds, provided that geometry and ensemble effects are included explicitly.
Hossam Elgabarty, T. D. Kühne· Journal of Physical Chemistr...· 0 citations
The present work revisits the methods within CP2K that turn electronic structure into dynamics, transport, and spectroscopic response, highlighting CP2K's unique capability to unify quantum chemistry with quantum and statistical mechanics within a versatile, holistic simulation environment.
Jan Wilhelm, Anna-Sophia Hehn, Hossam Elgabarty et al.· 1 citation· ⚡1
Stimulated by the renewed interest and recent developments in semiempirical quantum chemical (SQC) methods for noncovalent interactions, we examine the properties of liquid water under ambient conditions by means of molecular dynamics (MD) simulations, both with the conventional neglect of diatomic differential overlap-type methods, e.g., AM1 and PM6, and with DFTB-type (density-functional tight-binding) methods, e.g., DFTB2 and GFN-xTB (Geometry-Frequency-Noncovalent eXtended Tight-Binding). Besides the original parameter sets, some specifically reparameterized SQC methods (denoted as AM1-W, PM6-fm, and DFTB2-iBi) targeting various smaller water systems ranging from molecular clusters to bulk are considered as well. The quality of these different SQC methods for describing liquid water properties under ambient conditions is assessed by comparison with well-established experimental data and also with BLYP-D3 density functional theory-based ab initio MD simulations. Our analyses reveal that static and dynamic properties of bulk water are poorly described by all considered SQC methods with the original parameters, regardless of the underlying theoretical models, with most of the methods suffering from too weak hydrogen bonds and hence predicting a far too fluid water with highly distorted hydrogen bond kinetics. Meanwhile, the reparameterized force-matched PM6-fm method is shown to be able to quantitatively reproduce the static and dynamic features of liquid water and thus can be used as a computationally efficient alternative to electronic structure-based MD simulations for liquid water that requires extended length and time scales. DFTB2-iBi predicts a slightly overstructured water with reduced fluidity, whereas AM1-W gives an amorphous ice-like structure for water under ambient conditions.
Xin Wu, Hossam Elgabarty, Vahideh Alizadeh et al.· Journal of Chemical Physics· 1 citation
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