Chemical Physics Letters (v.573, #C)

Contents (iii-vii).

Bridging the macro and micro by R. Stephen Berry; Boris M. Smirnov (1-4).
This Letter uses one specific example and introduces a general approach to determining the effective limiting size, for any particular phenomenon, below which a microscopic approach is required, and above which one can use macroscopic formalisms such as traditional thermodynamics. The specific example is the determination of the size range of atomic clusters below which the Gibbs Phase Rule does not apply, because the free energy difference between favored and unfavored phases is small enough that the unfavored phase can be present in detectable amounts as a minority species under conditions of unequal free energies of two or more phases.A graphic illustration of phase coexistence for a cluster (lower figure) compared with a traditional phase diagram—but with an added dimension to reveal the coexistence range of two observable phases.A long-standing but rarely addressed challenge to physical sciences is reconciling or bridging between the macroscopic approach, exemplified by thermodynamics, continuum and infinite models, and the microscopic approach built from individual elements. Here, we show an approach to finding the boundary size region below which a microscopic approach is mandatory, and above which, one can use the macroscopic approach’s tools. We illustrate how to estimate this boundary size using examples from atomic clusters. The first reviews the boundary size above which the Gibbs Phase Rule is valid, but below, is inapplicable. Then we show how to find boundary sizes for other properties.

Characteristic pv → ppv transformation trajectory of MgSiO3 as obtained from transition path sampling iterations mimicking temperature and pressure conditions at planet Earth’s interior (D″ region).The atomistic mechanism of the perovskite → post-perovskite transformation of MgSiO3 is explored from molecular simulation mimicking extreme pressure and temperature conditions akin to planet Earth’s interior (D″ region). The nucleation process is highly anisotropic and initiated by column-wise rotation of SiO6 octahedra around the [0 0 1] direction. The post-perovskite transition is found to be a rare event (i.e. one requiring substantial activation energy, ∼15 eV for the critical nucleus, but, once started, propagates very fast (103–104  m/s). The most stable phase front, the (0 1 0) interface, propagates at only 10% of the speed of the (0 0 1) phase front.

Ab initio study of many-body decomposition of the interaction energy in small beryllium clusters Be 3 - 6 by Martin Šulka; Michal Pitoňák; Ivan Černušák; Miroslav Urban; Pavel Neogrády (8-14).
Display OmittedWe present the decomposition of interaction energies in beryllium clusters, Be m = 3 - 6 , into a series of nonidentical m-body nonadditivities up to m = 6 . We analyse the role of the electron correlation and compare nonadditivities at HF, CASSCF, MP2, CASPT2 and CCSD levels of theory with the reference aug-cc-pVTZ CCSD(T) results. The dominant nonadditivity terms are the three- and four-body. Five and six-body terms are relatively large in Be 5 - 6 clusters, but the total interaction energy of Be 6 is affected only marginally, due to their mutual cancellation.

The benzene–lithium complex is a prototype system to understand the interaction in lithium-doped nanocarbons. Herein, we have employed coupled-cluster theory and correlation consistent basis sets to study the C6v and C2v structures, of the C6H6·Li complex. We found that when the CCSD(T) method and large basis sets are employed, the C2V structure becomes lower in energy by 1.8 kcal/mol. At the CCSD(T)/CBS level, and including corrections for core–valence and relativistic effects, the dissociation energy of the C2v (ionic) structure is 6.7 kcal/mol whereas that corresponding to the C6v (nonionic) one is 4.9 kcal/mol. Our results suggest that charge transfer in C6H6·Li does exist, in contrast with previous results.

Display OmittedThe M06-2X and B2PLYP-D functionals have been applied to predict structures and energies for (CO2) n clusters up to n  = 16. A comparison between M06-2X, B2PLYP-D and benchmark CCSD(T) results indicates that M06-2X is capable of providing accurate binding energies. Stepwise M06-2X (CO2) n clustering free energies exhibit a sharp discontinuity at the magic cluster size n  = 13 and systematically shift to more exergonic values with decreasing temperature, in particular for larger clusters. These results indicate that the M06-2X method provides an accurate and cost effective description of non-covalent interactions in (CO2) n clusters and therefore may provide important information on CO2 nucleation phenomena.

Electron ionization of o-xylene, m-xylene and p-xylene by C.Q. Jiao; S.F. Adams (24-28).
Cross sections of electron ionization of three isomeric xylenes, in an electron energy range of 10–200 eV, are measured. The maximum total cross sections are observed at 80-eV electron energy to be 2.24, 2.10 and 2.05 × 10−15  cm2 for m-xylene, p-xylene and o-xylene, respectively. The xylene compounds produce similar ion populations, with major product ions including C8H7,9,10 +, C7H7 +, C6H5–7 +, C5H5 +, C4H3 + and C3H3 +. The similar ion populations can be explained through consideration of the fragmentation mechanism: essentially all fragment ions are formed via initial isomerization of the parent ions from the dimethylbenzene structures to the 7-methylcycloheptatriene structure.

Theoretical study on the electronic structures and phosphorescence properties of five osmium(II) complexes with different P^P ancillary ligands by Deming Han; Gang Zhang; Tian Li; Hongguang Li; Hongxing Cai; Xihe Zhang; Lihui Zhao (29-34).
The geometry structures, electronic structures, absorption, and phosphorescence properties of five heteroleptic cyclometalated osmium(II) complexes have been theoretically investigated. The lowest absorption of these complexes are located at 442, 441, 445, 439, and 446 nm, respectively, and the HOMO → LUMO or HOMO → LUMO + 1 is the predominant transitions. The lowest energy emissions of these complexes are localized at 620, 615, 616, 609 and 638 nm, respectively. Ionization potential (IP) and electron affinity (EA) have been calculated to evaluate the injection abilities of holes and electrons into these complexes. The reorganization energies indicate complex 5 has the best electron injection ability and electron-transporting performance.

Display OmittedThis letter definitely evaluates inner pressures of microbubbles in liquid argon and water by molecular dynamics simulation. The microbubbles are modeled with spherical cavity, which circumvents most uncertainties about microscopic definition of curved surface and related quantities. In both liquids, the inner pressure deviates downward from the Young–Laplace equation when the cavity radius is smaller than two molecular diameters, and takes a maximum, about 900 and 3000 atm, respectively, at the cavity radius being ∼3 Å. The hydrogen-bonding character of water plays little specific role in the deviation of the inner pressure.

Graphene decorated with Ni(OH)2 and Ag deposited Ni(OH)2 stacked nanoplate for supercapacitor application by Debasis Ghosh; Soumen Giri; Avinandan Mandal; Chapal Kumar Das (41-47).
Display OmittedIn this letter hydrothermally synthesized hierarchical stacked nanoplate of Ni(OH)2 and Ag deposited Ni(OH)2 have been successfully fabricated on graphene nanosheet. The prepared Ni(OH)2, Ag deposited Ni(OH)2 and their graphene based composites were characterized by XRD, FESEM and TEM analysis. Graphene increases the utility of the pseudocapacitive Ni(OH)2 and Ag deposited Ni(OH)2 as electrode material. Electrochemical characterizations in 6 M KOH electrolyte revealed superior electrode performance of the Ag deposited Ni(OH)2/graphene composite over Ni(OH)2/graphene composite with maximum specific capacitance of 496 F/g at 1 A/g current density accompanying 93% specific capacitance retention at the end of 500 consecutive charge discharge cycles.

Compression in encapsulated carboxylic acid homodimers by Demeter Tzeli; Ioannis D. Petsalakis; Giannoula Theodorakopoulos (48-55).
Display OmittedA density functional theory study has been carried out on five carboxylic acid homodimers, free and encapsulated, in order to study the effect of encapsulation or compression. Attractive interactions between the guests and the walls of the capsules stabilize encapsulation even in cases of severe confinement where formation of dimers is unfavorable. Larger hydrogen bonds are calculated for the encapsulated than the isolated dimers except for the case of the bulkiest dimer considered, where encapsulation leads to shortening of the hydrogen bond. Shorter hydrogen-bond lengths with increasing size of the encapsulated dimers are calculated, in agreement with experimental work.

Primary charge carrier dynamics of water-solubilized CdZnS/ZnS core/shell and CdZnS/ZnS·Pd nanoparticle adducts by Erik Busby; Arthur Thibert; Leah E. Page; Ali M. Jawaid; Preston T. Snee; Delmar S. Larsen (56-62).
The primary photodynamics of 5-nm CdZnS core, CdZnS/ZnS core/shell, and CdZnS/ZnS·Pd nanoparticle adducts are characterized with broadband ultrafast transient absorption spectroscopy. Photogenerated excitons in the CdZnS and CdZnS/ZnS nanoparticles exhibit long-lived (>20 ns) lifetimes and further functionalizing of the type-I CdZnS/ZnS core/shells with Pd nanoparticles resulted in rapid exciton quenching (<250 ps) due to the transfer of electrons from the CdZnS core into the Pd nanocrystals via tunneling through the insulating ZnS shell. The shell-induced surface trap passivation and near-unity charge carrier injection efficiency into a platinum-group metal nanoparticle shows potential for enhanced colloidal photocatalytic applications, while enhancing photostability.

Improvement of nonlinear response for the power conversion efficiency with light intensities in cobalt complex electrolyte system by Yong Hui Lee; Jin Hyuck Heo; Sang Hyuk Im; Hi-jung Kim; Choong-Sun Lim; Tae Kyu Ahn; Sang Il Seok (63-69).
Display OmittedA vertically aligned TiO2 photoelectrode with sufficient space between TiO2 nanorods was synthesized by sacrificial templating of ZnO nanorods grown on a dense TiO2 layer/FTO film. The more expanded pore space in the TiO2 nanorod film than conventional mesoscopic TiO2 film greatly reduces the mass transport problem of cobalt electrolyte in the vicinity of the Sb2S3 sensitizer in Sb2S3-sensitized photoelectrochemical solar cells. Therefore, the nonlinearity of the power conversion efficiency (PCE) under illumination intensity was greatly relieved to 5.0% (0.1 sun), 4.7% (0.5 sun), and 3.7% (1 sun) in a TiO2-nanorod-based Sb2S3-sensitized solar cell, whereas the efficiency of a mesoscopic-TiO2-based solar cell was significantly degraded to 5.3% (0.1 sun), 3.8% (0.5 sun), and 2.3% (1 sun).

Display OmittedThe structures of small Pd–Au clusters adsorbed on stepped MgO(1 0 0) are studied by Density-Functional Theory calculations, in the size range from 2 to 7 atoms for all compositions. A series of different structural motifs is singled out. These motifs are often in close energetic competition. It is shown that the adsorption in the vicinity of a step has strong effects on the preferential morphologies of these clusters. The driving forces for the stabilization of the lowest-energy structures are discussed.

Display OmittedThe equation-of-motion phase-matching approach provides an efficient way for calculating a system’s time-dependent polarization in any phase-matching direction subject to weak laser fields of arbitrary shape. Within this approach, we introduce the Poisson Bracket Mapping Equation and Forward–Backward methods, two approximate solutions of the quantum–classical Liouville equation, for simulating the laser-induced response of a quantum subsystem in a classical environment. We illustrate this approach by calculating the transient absorption signal in a model photo-induced condensed phase electron transfer reaction. The results are found to be in reasonable agreement with the exact results, which is promising for applications to realistic systems.

We propose a new scheme for the direct diabatization of MC-QDPT wave functions. Our new scheme utilizes CASSCF diabatic molecular orbitals (DMOs); this is conceptually simpler than the previous approach and can lead to smoother diabatic potentials. We validated the new diabatization scheme, in comparison to CASSCF diabatization and to the original MC-QDPT diabatization scheme, for two test cases, the dissociation of LiF and the reaction of Li + FH → LiF + H. The results with our new scheme suggest that the new scheme with CASSCF DMOs would be a good choice for nonadiabatic dynamics studies in the future.