The method of dispersion correction as an add-on to standard Kohn-Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C(6) coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/J%20Che%20Phy132,%20154104.pdf

A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited

Optical second-harmonic generation and the related technique of infrared – visible light sum-frequency generation are extremely versatile tools for studies of many kinds of surfaces and interfaces. With the help of ultra-short laser pulses, they can be used to monitor surface dynamics and reactions with sub-picosecond time resolution.

Surface properties probed by second-harmonic and sum-frequency generation

Catalysis plays a critical role in chemical conversion, energy production and pollution mitigation. High activation barriers associated with rate-limiting elementary steps require most commercial heterogeneous catalytic reactions to be run at relatively high temperatures, which compromises energy efficiency and the long-term stability of the catalyst. Here we show that plasmonic nanostructures of silver can concurrently use low-intensity visible light (on the order of solar intensity) and thermal energy to drive catalytic oxidation reactions--such as ethylene epoxidation, CO oxidation, and NH₃ oxidation--at lower temperatures than their conventional counterparts that use only thermal stimulus. Based on kinetic isotope experiments and density functional calculations, we postulate that excited plasmons on the silver surface act to populate O₂ antibonding orbitals and so form a transient negative-ion state, which thereby facilitates the rate-limiting O₂-dissociation reaction. The results could assist the design of catalytic processes that are more energy efficient and robust than current processes.

Visible-light-enhanced catalytic oxidation reactions on plasmonic silver nanostructures

(Contents for Vols 1 & 2) Part 1 Spectroscopy and diagnostics: sum-frequency generation as a surface probe, JY Huang and YR Shen second harmonic generation from metal surfaces, A Liebsch two-photon photoelectron spectroscopy of electronic states at metal surfaces, W Steinmann and T Fauster Part 2 Energy transfer dynamics: ultrafast hot electron relaxation in metals, J Bokor and WS Fann surface vibrational dynamics probed by sum frequency generation, P Guyot-Sionnest and AL Harris laser heating and time resolved measurements of transient temperature changes on surfaces, JM Hicks Part 3 Desorption dynamics: electronically stimulated desorption of neutrals and ions from adsorbed and condensed layers, P Feulner and D Menzel laser induced desorption, Y Murata and K Fukutani femtosecond surface science - the dynamics of desorption, TF Heinz et al hot electrons and photodesorption dynamics - theory, JW Gadzuk hydrogen recombinative desorption dynamics, RN Zare et al photochemistry - photodissociation and photoreaction of molecules attached to metal surfaces, X-L Zhou and JM White dynamics of adsorbate photochemistry, JC Polanyi and Y Zeiri (Part Contents)

Laser spectroscopy and photochemistry on metal surfaces

Since the first stimulated emission pumping (SEP) experiments more than a decade ago, this technique has proven powerful for studying vibrationally excited molecules. SEP is now widely used by increasing numbers of research groups to investigate fundamental problems in spectroscopy, intramolecular dynamics, intermolecular interactions, and even reactions. SEP provides rotationally pre-selected spectra of vibrationally highly excited molecules undergoing large amplitude motions. A unique feature of SEP is the ability to access systematically a wide variety of extreme excitations localized in various parts of a molecule, and to prepare populations in specific, high vibrational levels. SEP has made it possible to ask and answer specific questions about intramolecular vibrational redistribution and the role of vibrational excitation in chemical reactions.

Molecular dynamics and spectroscopy by stimulated emission pumping

The dynamics of excited carriers generated near a silicon surface were characterized on femtosecond time scales using the transient grating technique in the reflection configuration. For electrons in the energy range $1.4\ifmmode\pm\else\textpm\fi{}0.6\mathrm{eV}$ above the conduction band edge and their corresponding holes, the lifetime for relaxation through phonon scattering at carrier densities below ${10}^{20}\phantom{\rule{0ex}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ was determined to be 240 fs. This relaxation time increased sharply for carrier densities higher than $5\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{0ex}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, providing the first direct evidence for charge screening of carrier-phonon scattering in Si.

Ultrafast Carrier Dynamics in Silicon: A Two-Color Transient Reflection Grating Study on a ( 111 ) Surface

Small aluminum nanoparticles have the potential to exhibit localized surface plasmon resonances in the deep ultraviolet region of the electromagnetic spectrum, however technical and scientific challenges make it difficult to attain this limit. We report the fabrication of arrays of Al/Al2O3 core/shell nanoparticles with a metallic-core diameter between 12 and 25 nm that display sharp plasmonic resonances at very high energies, up to 5.8 eV (down to λ = 215 nm). The arrays were fabricated by means of a straightforward self-organization approach. The experimental spectra were compared with theoretical calculations that allow the correlation of each feature to the corresponding plasmon modes.

Deep ultraviolet plasmon resonance in aluminum nanoparticle arrays.

A complete set of 27 normal mode vibrational constants ω0 i and x i  j as well as six harmonized vibrational frequencies ω i is obtained for the H2CO X1 A 1 state: ω0 1 =2811.42(15), ω0 2 =1755.858(40), ω0 3 =1500.32(49), ω0 4 =1170.224(30), ω0 5 =2861.30(14), ω0 6 =1250.565(63) x 1 1=−28.95(14), x 1 2=1.15(19), x 1 3=−23.03(14), x 1 4=−10.099(65), x 1 5=−193.32(24), x 1 6=−49.78(33) x 2 2=−9.926(23), x 2 3=−8.26(11), x 2 4=−7.199(39), x 2 5=−17.23(23), x 2 6=6.581(49), x 3 3=−0.164(97), x 3 4=−1.769(52), x 3 5=6.00(37), x 3 6=−29.861(88), x 4 4=−3.157(12), x 4 5=−13.35(17), x 4 6=−2.860(70) x 5 5=−17.97(13), x 5 6=−17.63(33), x 6 6=−1.567(56), ω1=2977.91(31), ω2=1778.26(16), ω3=1528.95(54), ω4=1191.02(11), ω5=2997.04(36), ω6=1298.91(26) (1σ uncertainty in parentheses). These vibrational constants are derived primarily from stimulated emission pumping (SEP) spectra of more than 50 4500–9300 cm− 1 vibrational levels of the X1 A 1 state, supplemented by partial rotational analyses of 12 4000–8100 cm− 1FTIR overtone and combination bands. This is the first time that the SEP technique has been systematically applied to a traditional but seldom achievable objective of high resolution vibrational spectroscopy, determination of a complete set of ω0 i and x i  j constants. Insofar as the rotationless vibrational levels of H2CO X1 A 1 can each be unambiguously assigned a set of normal mode quantum numbers and reproduced by a minimal set of vibrational constants, the X state of formaldehyde remains vibrationally well organized up to at least 9300 cm− 1.

Hai-Lung Dai

Papers

Laser spectroscopy and photochemistry on metal surfaces

Molecular dynamics and spectroscopy by stimulated emission pumping

Ultrafast Carrier Dynamics in Silicon: A Two-Color Transient Reflection Grating Study on a ( 111 ) Surface

Deep ultraviolet plasmon resonance in aluminum nanoparticle arrays.

Stimulated emission spectroscopy: A complete set of vibrational constants for X̃ 1A1 formaldehyde