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How Water's Properties Are Encoded in Its Molecular Structure and Energies.
How are water's material properties encoded within the structure of the water molecule? This is pertinent to understanding Earth's living systems, its materials, its geochemistry and geophysics, and a broad spectrum of its industrial chemistry. Water has distinctive liquid and solid properties: It is highly cohesive. It has volumetric anomalies-water's solid (ice) floats on its liquid; pressure can melt the solid rather than freezing the liquid; heating can shrink the liquid. It has more solid phases than other materials. Its supercooled liquid has divergent thermodynamic response functions. Its glassy state is neither fragile nor strong. Its component ions-hydroxide and protons-diffuse much faster than other ions. Aqueous solvation of ions or oils entails large entropies and heat capacities. We review how these properties are encoded within water's molecular structure and energies, as understood from theories, simulations, and experiments. Like simpler liquids, water molecules are nearly spherical and interact with each other through van der Waals forces. Unlike simpler liquids, water's orientation-dependent hydrogen bonding leads to open tetrahedral cage-like structuring that contributes to its remarkable volumetric and thermal properties
Calculation of Linear and Non-linear Electric Response Properties of Systems in Aqueous Solution: A Polarizable Quantum/Classical Approach with Quantum Repulsion Effects
We present a computational study of polarizabilities and hyperpolarizabilities of organic molecules in aqueous solutions, focusing on solute-water interactions and the way they affect a molecule's linear and non-linear electric response properties. We employ a polarizable quantum mechanics/molecular mechanics (QM/MM) computational model that treats the solute at the QM level while the solvent is treated classically using a force field that includes polarizable charges and dipoles, which dynamically respond to the solute's quantum-mechanical electron density. Quantum confinement effects are also treated by means of a recently implemented method that endows solvent molecules with a parametric electron density, which exerts Pauli repulsion forces upon the solute. By applying the method to a set of aromatic molecules in solution we show that, for both polarizabilities and first hyperpolarizabilities, observed solution values are the result of a delicate balance between electrostatics, hydrogen-bonding, and non-electrostatic solute solvent interactions
Water alignment, dipolar interactions, and multiple proton occupancy during water-wire proton transport
A discrete multistate kinetic model for water-wire proton transport is
constructed and analyzed using Monte-Carlo simulations. The model allows for
each water molecule to be in one of three states: oxygen lone pairs pointing
leftward, pointing rightward, or protonated (HO). Specific rules
for transitions among these states are defined as protons hop across successive
water oxygens. We then extend the model to include water-channel interactions
that preferentially align the water dipoles, nearest-neighbor dipolar coupling
interactions, and coulombic repulsion. Extensive Monte-Carlo simulations were
performed and the observed qualitative physical behaviors discussed. We find
the parameters that allow the model to exhibit superlinear and sublinear
current-voltage relationships and show why alignment fields, whether generated
by interactions with the pore interior or by membrane potentials {\it always}
decrease the proton current. The simulations also reveal a ``lubrication''
mechanism that suppresses water dipole interactions when the channel is
multiply occupied by protons. This effect can account for an observed
sublinear-to-superlinear transition in the current-voltage relationship
Noncovalent Bonds through Sigma and Pi-Hole Located on the Same Molecule. Guiding Principles and Comparisons
Over the last years, scientific interest in noncovalent interactions based on the presence of electron-depleted regions called σ-holes or π-holes has markedly accelerated. Their high directionality and strength, comparable to hydrogen bonds, has been documented in many fields of modern chemistry. The current review gathers and digests recent results concerning these bonds, with a focus on those systems where both σ and π-holes are present on the same molecule. The underlying principles guiding the bonding in both sorts of interactions are discussed, and the trends that emerge from recent work offer a guide as to how one might design systems that allow multiple noncovalent bonds to occur simultaneously, or that prefer one bond type over another
From Andreev to Majorana bound states in hybrid superconductor-semiconductor nanowires
Electronic excitations above the ground state must overcome an energy gap in
superconductors with spatially-homogeneous s-wave pairing. In contrast,
inhomogeneous superconductors such as those with magnetic impurities or weak
links, or heterojunctions containing normal metals or quantum dots, can host
subgap electronic excitations that are generically known as Andreev bound
states (ABSs). With the advent of topological superconductivity, a new kind of
ABS with exotic qualities, known as Majorana bound state (MBS), has been
discovered. We review the main properties of ABSs and MBSs, and the
state-of-the-art techniques for their detection. We focus on hybrid
superconductor-semiconductor nanowires, possibly coupled to quantum dots, as
one of the most flexible and promising experimental platforms. We discuss how
the combined effect of spin-orbit coupling and Zeeman field in these wires
triggers the transition from ABSs into MBSs. We show theoretical progress
beyond minimal models in understanding experiments, including the possibility
of different types of robust zero modes that may emerge without a
band-topological transition. We examine the role of spatial non-locality, a
special property of MBS wavefunctions that, together with non-Abelian braiding,
is the key to realizing topological quantum computation.Comment: Review. 23 pages, 8 figures, 1 table. Shareable published version by
Springer Nature at https://rdcu.be/b7DWT (free to read but not to download
The electronic origin of the ground state spectral features and excited state deactivation in cycloalkanones: the role of intermolecular H-bonding in neat and binary mixtures of solvents
In this study, a D-A cycloalkanone (K1) has been investigated by steady state absorption and fluorescence in neat solvents and in three binary mixtures of nonpolar aprotic/polar protic, polar aprotic/polar protic, and polar protic/polar protic solvents. The experimental findings were complemented by density functional theory (DFT), time-dependent density functional theory (TD-DFT), and NBO quantum-mechanical calculations. Experimentally, effective changes in absorption and fluorescence were observed by solute-solvent interaction. The binary K1-solvent1-solv2 configuration, modeled at the B3LYP-DFT level, confirms involvement of inter-molecular H-bonding with the carbonyl C=O in the fluorescence deactivation process (quenching). This is supported by considerable electron delocalization from C=O to the solvent's hydroxyl (nO????*H-O). This type of hyperconjugation was found to be the main driver for solute-solvent stabilization.Scopu
A Non-Perturbative Pairwise-Additive Analysis of Charge Transfer Contributions to Intermolecular Interaction Energies
Energy decomposition analysis (EDA) based on absolutely localized molecular
orbitals (ALMOs) decomposes the interaction energy between molecules into
physically interpretable components like geometry distortion, frozen
interactions, polarization, and charge transfer (CT, also sometimes called
charge delocalization) interactions. In this work, a numerically exact scheme
to decompose the CT interaction energy into pairwise additive terms is
introduced for the ALMO-EDA using density functional theory. Unlike
perturbative pairwise charge-decomposition analysis, the new approach does not
break down for strongly interacting systems, or show significant
exchange-correlation functional dependence in the decomposed energy components.
Both the energy lowering and the charge flow associated with CT can be
decomposed. Complementary occupied-virtual orbital pairs (COVPs) that capture
the dominant donor and acceptor CT orbitals are obtained for the new
decomposition. It is applied to systems with different types of interactions
including DNA base-pairs, borane-ammonia adducts, and transition metal
hexacarbonyls. While consistent with most existing understanding of the nature
of CT in these systems, the results also reveal some new insights into the
origin of trends in donor-acceptor interactions
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