The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

The hydrogen bond in the solid state.

"Chemists familiar with conventional quantum mechanics will applaud and benefit greatly from this particularly instructive, thorough and clearly written exposition of density functional theory: its basis, concepts, terms, implementation, and performance in diverse applications. Users of DFT for structure, energy, and molecular property computations, as well as reaction mechanism studies, are guided to the optimum choices of the most effective methods. Well done!" Paul von RaguE Schleyer "A conspicuous hole in the computational chemist's library is nicely filled by this book, which provides a wide-ranging and pragmatic view of the subject.[...It] should justifiably become the favorite text on the subject for practioneers who aim to use DFT to solve chemical problems." J. F. Stanton, J. Am. Chem. Soc. "The authors' aim is to guide the chemist through basic theoretical and related technical aspects of DFT at an easy-to-understand theoretical level. They succeed admirably." P. C. H. Mitchell, Appl. Organomet. Chem. "The authors have done an excellent service to the chemical community. [...] A Chemist's Guide to Density Functional Theory is exactly what the title suggests. It should be an invaluable source of insight and knowledge for many chemists using DFT approaches to solve chemical problems." M. Kaupp, Angew. Chem.

A Chemist's Guide to Density Functional Theory

6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

Noncovalent interactions: a challenge for experiment and theory

We present calculations for the nonbonded interactions in the dimeric complexes:  methane dimer, ammonia dimer, water dimer, H2O·(NH3), CH4·(NH3), and (FHF)- as a function of theory level (HF, DFT(B3LYP), MP2, LMP2, MP3, MP4, CCSD(T), and others) and basis set (6-31G**, cc-pVXZ, X = D, T, Q, 5). Dimer minimum energy structures are determined at the MP2 theory level for the cc-pVTZ basis set employing analytical second derivatives. For HF and DFT levels of theory, methane dimer and one structure of CH4·(NH3) are not bound. The basis set superposition error (BSSE) begins to converge (becomes systematically small) for basis sets larger than cc-pVTZ. For hydrogen-bonded systems, most levels of theory seem to give reasonable estimates of the experimentally known binding energies, but here, too, the BSSE overwhelms the reliability of the binding energies for the smaller basis sets. The CH4·(NH3) dimer has two minimum energy conformations with similar binding energies, but very different BSSE values especially f...

/pdf/ab-initio-calculation-of-nonbonded-interactions-are-we-there-3zojby9thi.pdf

Ab Initio Calculation of Nonbonded Interactions: Are We There Yet?

The optical absorption spectra of the first excited singlet states of the benzene, toluene, and toluene–benzene dimers, created in a supersonic molecular jet, are reported. The absorption spectra are detected through two‐color time of flight mass spectroscopy; this method eliminates fragmentation of dimers and higher clusters and the dimer spectra are uniquely observed. The benzene dimer observed in this experiment is suggested to have a parallel stacked and displaced configuration of C2h symmetry. Both the toluene and toluene–benzene dimers have two configurations: parallel stacked and displaced [based on (benzene)2] and perpendicular. (Benzene)2, (toluene)2, and toluene–benzene form excimers in the excited state for the parallel stacked displaced configurations. The transformation of (benzene)2 to the excimer takes place at the 00 with a ∼0 cm−1 barrier while the excimer is formed for toluene–benzene with a ∼900 cm−1 barrier. An exciton analysis of the (benzene)2 000 and 610 yields M12, the excitation e...

Dimers of aromatic molecules: (Benzene)2, (toluene)2, and benzene–toluene

We have demonstrated a new type of high repetition rate 46.9 nm capillary discharge laser that fits on top of a small desk and that it does not require a Marx generator for its excitation. The relatively low voltage required for its operation allows a reduction of nearly one order of magnitude in the size of the pulsed power unit relative to previous capillary discharge lasers. Laser pulses with an energy of ~ 13 microJ are generated at repetition rates up to 12 Hz. About (2-3) x 10 4 laser shots can be generated with a single capillary. This new type of portable laser is an easily accessible source of intense short wavelength laser light for applications.

/pdf/demonstration-of-a-desk-top-size-high-repetition-rate-soft-x-1z6y3n5v6c.pdf

Demonstration of a desk-top size high repetition rate soft x-ray laser based on a fast capillary discharge

Dispersed emission and time of flight mass spectra are presented for jet‐cooled toluene, and o‐, m‐, and p‐xylene. The spectra exhibit features, typically within 100 cm−1 of the S1⇄S0 origins, which are assigned to transitions associated with the internal rotation of the ring methyl groups. A model is developed which treats this methyl motion as that of a one‐dimensional rigid rotor. The spacings of the peaks in the spectra are used to solve for the rotational constant B of the methyl rotor, and for the size and shape of the n‐fold barrier to rotation (i.e., V3, V6, etc.) within this model. For toluene and p‐xylene, the barrier is found to be small in both the ground (S0) (V6∼10 cm−1) and excited (S1) (V6∼25 cm−1) electronic states. For m‐xylene, the ground state is again found to have a low barrier (V6∼25 cm−1), but the excited state has a potential barrier of V3=81 cm−1, V6=−30 cm−1. The barrier to rotation of the ring methyl groups is observed to be the highest for o‐xylene. In this case the ground sta...

A study of nonrigid aromatic molecules by supersonic molecular jet spectroscopy. I. Toluene and the xylenes

More than a dozen cases of nonrigid van der Waals clusters are presented and discussed to demonstrate that cluster nonrigidity is a general phenomenon in all weakly bound systems. The interplay of structure and nonrigidity complicates cluster research and mandates a dynamical approach to cluster properties in which multiple stable configurations coexist and interconvert, and large amplitude nuclear motions are the rule rather than the exception. Empirical potential energy surface calculations are employed to yield physical insight into the structure and dynamics of nonrigid clusters, and molecular symmetry group theory is applied to analyze spectroscopic manifestations of cluster nonrigidity. Empirical potentials of various forms are successful in predicting most cluster structures, as well as estimating the potential surface barrier heights hindering the interconversion between different local minimum-energy structures. Such calculational approaches also emphasize the importance of large amplitude motion...

Elliot R. Bernstein

Papers

Ab Initio Calculation of Nonbonded Interactions: Are We There Yet?

Dimers of aromatic molecules: (Benzene)2, (toluene)2, and benzene–toluene

Demonstration of a desk-top size high repetition rate soft x-ray laser based on a fast capillary discharge

A study of nonrigid aromatic molecules by supersonic molecular jet spectroscopy. I. Toluene and the xylenes

Aromatic van der Waals Clusters: Structure and Nonrigidity