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Considering the significant threat of heat to electronic equipment and the heat dissipation problems existing in powerful systems, thermal management materials are in high demand. In conjunction with the increasing desire of dissipating heat and stabilizing temperature, high thermal conductivity and phase change latent heat are attracting more attention when designing thermal management material. This work proposes a strategy to combine phase change matrix and thermally conductive filler using freeze casting. The highest thermal conductivity reaches 23.1 W m-1 K-1 accompanied by 62 J g-1 phase change latent heat. Meanwhile, replacing ice with organic phase change material in freeze casting can result in an aligned structure. This discovery will pave a novel way for introducing thermal latent heat without abandoning the aligned structure.

The interfacial contacts between the electron transporting layers (ETLs) and the photoactive layers are crucial to device performance and stability for OSCs with inverted architecture. Herein, atomic layer deposition (ALD) fabricated ultrathin Al2O3 layers are applied to modify the ETLs/active blends (PM6:BTP-BO-4F) interfaces of OSCs, thus improving device performance. The ALD-Al2O3 thin layers on ZnO significantly improved its surface morphology, which led to the decreased work function of ZnO and reduced recombination losses in devices. The simultaneous increase in open-circuit voltage (), short-circuit current density () and fill factor (FF) were achieved for the OSCs incorporated with ALD-Al2O3 interlayers of a certain thickness, which produced a maximum PCE of 16.61%. Moreover, the ALD-Al2O3 interlayers had significantly enhanced device stability by suppressing degradation of the photoactive layers induced by the photocatalytic activity of ZnO and passivating surface defects of ZnO that may play the role of active sites for the adsorption of oxygen and moisture.

(Figure Presented) We present calculations of electronic structure properties of disordered conducting polymers containing thieno[3,2b]thiophene, diketopyrrolopyrrole, and thiophene. Atomistic force field parameters for the polymer were optimized to minimize the difference between the ab initio and empirical potential energy surfaces and their corresponding first derivatives. These new force fields are employed to propagate the nuclear dynamics, and the equilibrium trajectories are sampled for subsequent electronic structure calculations. We found that the fluctuations of the bulk density of states are negligibly small and do not vary significantly with the length of the backbone and the side-chains. The localization length near the band gap is between 8 and 12 Å, which is about half of the length of the monomer and significantly less than the length of the extended polymer (∼200−400 Å). This indicates that the orbital localization is not affected by the length of the polymer. The inter-chain excitonic couplings are usually smaller than 5 meV, suggesting that the transport mechanism across chains is described by incoherent hopping, and excitons mainly move along the chain. Furthermore, thermal fluctuations cause the evolution of the excitons along the chain. Characterization of the relationships between the geometric disorder of the polymers and the distributions of the lowest excited states reveals that the low-energy excitons tend to localize in regions that are more planar and less folded. However, some excitons are also spread over defects. Thus, our theoretical calculations and the new force fields provide a direct route for characterizing the structure−property relationships and helpful information for constructing more realistic models for the exciton dynamics study of this class of polymeric materials.

Utilizing a force-matching procedure, we parametrize new force fields systematically for large conjugated systems. We model both conjugated polymers and molecular crystals that contain diketopyrrolopyrrole, thiophene, and thieno[3,2-b]thiophene units. These systems have recently been found to have low band gaps, which exhibit high efficiency for photovoltaic devices. The equilibrium structures, forces, and energies of the building block chromophores, diketopyrrolopyrrole, thiophene, and thieno[3,2-b]thiophene computed using our parameters are comparable to those computed using the reference electronic structure method. We assess the suitability of this new force field for electronic property calculations by comparing the electronic excitation properties computed along classical and ab initio molecular dynamics trajectories. For both trajectories, we find similar distributions of TDDFT-calculated excitation energies and oscillator strengths for the building block chromophore diketopyrrolopyrrole-thieno[3,2-b]thiophene. The structural, dynamic, and electronic properties of the macromolecular assemblies built upon these chromophores are characterized. For both polymers and molecular crystals, pronounced peaks around 0° or 180° are observed for the torsions between chromophores under ambient conditions. The high planarity in these systems can promote local ordering and π–π stacking, thereby potentially facilitating charge transport across these materials. For the model conducting polymers, we found that the fluctuations in the density of states per chain per monomer is negligibly small and does not vary significantly with chains comprising 20–40 monomers. Analysis of the electron–hole distributions and the transition density matrices indicates that the delocalized length is approximately 4–6 monomers, which is in good agreement with other theoretical and experimental studies of different conducting polymers. For the molecular crystals, our investigation of the characteristic time scale of the fluctuation in the excitonic couplings shows that a low-frequency vibration below 100 cm–1 is observed for the nearest neighbors. These observations are in line with previous studies on other molecular crystals, in which low-frequency vibrations are believed to be responsible for the large modulation of the excitonic coupling. Thus, our approach and the new force fields provide a direct route for studying the structure–property relations and the molecular level origins of the high efficiency of these classes of materials.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design. This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design.

We present a concise, general, and efficient procedure for calculating the cluster integrals that relate thermodynamic virial coefficients to molecular interactions. The approach encompasses nonpairwise intermolecular potentials generated from quantum chemistry or other sources; a simple extension permits efficient evaluation of temperature and other derivatives of the virial coefficients. We demonstrate with a polarizable model of water. We argue that cluster-integral methods are a potent yet underutilized instrument for the development and application of first-principles molecular models and methods.

Enabling efficient and durable charge storage under high sulfur loading and lean electrolyte remains a paramount challenge for Li-S battery technology to truly demonstrate its commercial viability. This work reports an amphoteric polymer binder, whose negatively and positively charged moieties allow for coregulation of both lithium cations and heteropolar lithium polysulfides through multiple intermolecular interactions. These interactions and the physical properties lead to simultaneously improved Li

Molybdenum disulfide (MoS2) monolayers with tertiary N atoms surrounding the single Mo-vacancy sites (MoS2_1VMo_3NS) sites have been found to exhibit outstanding adsorption activity and stability. While previous literature suggested the enhanced physical adsorption nature of CO2, N2 and H2O molecules on MoS2_1VMo_3NS sites due to promotional effects of tertiary nitrogen doping of 1 Mo-vacancy, this work highlights the adsorption and dissociation of CO2 and H2O on MoS2_1VMo_3NS sites, which are investigated using density functional theory (DFT). Compared with pure MoS2 (PMoS2), our DFT calculations reveal that the MoS2_1VMo_3NS are the most catalytically active sites. The interactions with CO2 and H2O are enhanced by the larger electron distribution with N dopants and neighboring S atoms. Climbing image nudged elastic band (Cl-NEB) and ab initio molecular dynamics (AIMD) analyses indicate that the interactions are exothermic and result in spontaneous molecular dissociation. Here, CO2 dissociates into CO* and O* on two N atoms with free energy barrier (ΔGa) of −0.27 eV; while H2O dissociates via two mechanisms: (1) into adsorbed OH* and H* species (ΔGa = 0.21 eV), and (2) into adsorbed O, H, H atoms (ΔGa = 0.10 eV). The computed ΔGa values are significantly lower than the threshold energy barrier for chemical reactions at room temperature (0.8 eV), which also indicates that CO2 and H2O dissociation is spontaneous at ambient temperature. This study shows the immense potential of MoS2_1VMo_3NS in the sustainable production of fuels and chemicals via the highly efficient dissociation of inert CO2 and H2O.

Three new boron dipyrromethene (BODIPY) dyes substituted with a benzylamino group at the 3-position have been synthesized from halogenated BODIPYs by nucleophilic substitution. The spectroscopic and photophysical properties have been explored in different solvents and have been compared with an analogous 8- benzylaminoBODIPY derivative. The position of the benzylamino group has a significant influence on the spectral band positions, fluorescence quantum yields, and fluorescence lifetimes. The 8- benzylaminoBODIPY emits in the blue range, whereas the 3- substituted shows green fluorescence. Additionally, the extension of the conjugation at the 5-position of 3-benzylaminoBODIPY produces a bathochromic shift of the absorption and emission spectra. The solvent effect on their spectroscopic features has been investigated using the generalized Catalan solvent scales. Quantum-chemical calculations have been performed to assess the effect of the position of the substitution on the spectroscopic properties. Finally, the BODIPY dyes have been employed as probes in fluorescence lifetime imaging of living cells, demonstrating their high potential for bioimaging.

Thermal interface materials (TIM) have become a leading solution to achieve lower operating temperature in electronic devices. To improve thermal conductivity and to simultaneously reduce thermal resistance, this work investigates the thermal properties for interface materials with carbon fiber and graphite. When the ratio between carbon fiber to graphite is 1:1, the thermal resistance can be reduced to 1.8 × 10−4 K m2 W−1 at 30 psi, although the bulk thermal conductivity is lowered from 34 to 19 W m−1 K−1. The synergistic effect between carbon fiber and graphite is investigated. Surface roughness of TIMs was measured and two different types of thermal conductivity measurement were applied to demonstrate that graphite makes a contribution to bulk thermal conductivity where a CF played an important role for smoothing the surface, thereby lowering the thermal resistance. In real applications, the hybrid filler is shown to perform better in enhancing the heat conduction for electrical packaging.

The space within the interlayer of 2-dimensional (2D) nanosheets provides new and intriguing confined environments for molecular interactions. However, atomic level understanding of the adsorption mechanism of CO2 confined within the interlayer of 2D nanosheets is still limited. Herein, we present a comparative study of the adsorption mechanisms of CO2 confined within graphene–molybdenum disulfide (MoS2) nanosheets using density functional theory (DFT). A comprehensive analysis of CO2 adsorption energies (EAE) at various interlayer spacings of different multilayer structures comprising graphene/graphene (GrapheneB) and MoS2/MoS2 (MoS2B) bilayers as well as graphene/MoS2 (GMoS2) and MoS2/graphene (MoS2G) hybrids is performed to obtain the most stable adsorption configurations. It was found that 7.5 A and 8.5 A interlayer spacings are the most stable conformations for CO2 adsorption on the bilayer and hybrid structures, respectively. Adsorption energies of the multilayer structures decreased in the following trend: MoS2B > GrapheneB > MoS2G > GMoS2. By incorporating van der Waals (vdW) interactions between the CO2 molecule and the surfaces, we find that CO2 binds more strongly on these multilayer structures. Furthermore, there is a slight discrepancy in the binding energies of CO2 adsorption on the heterostructures (GMoS2, MoS2G) due to the modality of the atom arrangement (C–Mo–S–O and Mo–S–O–C) in both structures, indicating that conformational anisotropy determines to a certain degree its CO2 adsorption energy. Meanwhile, Bader charge analysis shows that the interaction between CO2 and these surfaces causes charge transfer and redistributions. By contrast, the density of states (DOS) plots show that CO2 physisorption does not have a substantial effect on the electronic properties of graphene and MoS2. In summary, the results obtained in this study could serve as useful guidance in the preparation of graphene–MoS2 nanosheets for the improved adsorption efficiency of CO2.

Polymer composites that have high thermal conductivity have become one of the most promising solutions needed to satisfy the thermal management requirements for high-power electrical and electronic equipment. In this work, a strategy relying on aligning carbon fibers through the application of a stress field is proposed. Ultrahigh through-plane thermal conductive epoxy composites with carbon fiber networks have been prepared by in-situ solidification within an epoxy. The thermal conductivity of these epoxy composites reaches as high as 32.6 W m−1 K−1 at 46 wt percent (wt%) of carbon fibers, which is about 171 times that of the pure epoxy. The alignment condition for the carbon fibers for a carbon fiber composite in which stress has been applied and a blended carbon fiber composite are compared using micro compute tomography (micro-CT) and scanning electron microscopy (SEM). These epoxy composites display attractive thermal properties and provide a practical route to satisfy the thermal dissipation requirements raised by the development of modern electrical devices and systems.

A density functional theory study was conducted to analyze CO2 adsorption on defective and non-defective MoS2 surfaces with or without nitrogen doping. The MoS2_1VS and MoS2_1VMo_3NS were found exhibiting outstanding adsorption activity and stability, which is linked to an enhanced electron charge on the surface in the presence of vacancies and N species that alters strength and type of interactions with CO2 molecules. Results showed the dissociative chemisorption of CO2 on the MoS2_1Vs and a significantly enhanced physisorption of CO2 on the MoS2_1VMo_3NS, which displays an adsorption energy of −1.818 eV compared with −0.139 eV of the pristine MoS2 surface. Meanwhile, the MoS2_1Vs exhibits an excellent selective adsorption of CO2 over N2 and H2O, with the highest adsorption ratio of 5.1 and 3.5, respectively. Partial dissociation of CO2 to CO over the MoS2_1Vs is also observed and attributed to increased covalent attractions at the vacant site, while the improved CO2 physisorption over the MoS2_1VMo_3NS is attributed to the enhanced electrostatic interactions at the vacancy site due to N doping. These findings are confirmed by the computed vibrational frequencies of CO2 bound on these surfaces. The N-doping enabled defect engineering of MoS2 is proved effective and enhanced selective adsorption of CO2.

This paper reviews the current technological development of bio-hydrogen (BioH2) generation, focusing on using lignocellulosic feedstock via dark fermentation (DF). Using the collected reference reports as the training data set, supervised machine learning via the constructed artificial neuron networks (ANNs) imbedded with feed backward propagation and one cross-out validation approach was deployed to establish correlations between the carbon sources (glucose and xylose) together with the inhibitors (acetate and other inhibitors, such as furfural and aromatic compounds), hydrogen yield (HY), and hydrogen evolution rate (HER) from reported works. Through the statistical analysis, the concentrations variations of glucose (F-value = 0.0027) and acetate (F-value = 0.0028) were found to be statistically significant among the investigated parameters to HY and HER. Manipulating the ratio of glucose to acetate at an optimal range (approximate in 14:1) will effectively improve the BioH2 generation (HY and HER) regardless of microbial strains inoculated. Comparative studies were also carried out on the evolutions of electron equivalent balances using lignocellulosic biomass as substrates for BioH2 production across different reported works. The larger electron sinks in the acetate is found to be appreciably related to the higher HY and HER. To maintain a relative higher level of the BioH2 production, the biosynthesis needs to be kept over 30% in batch cultivation, while the biosynthesis can be kept at a low level (2%) in the continuous operation among the investigated reports. Among available solutions for the enhancement of BioH2 production, the selection of microbial strains with higher capacity in hydrogen productions is still one of the most phenomenal approaches in enhancing BioH2 production. Other process intensifications using continuous operation compounded with synergistic chemical additions could deliver additional enhancement for BioH2 productions during dark fermentation.

The space within the interlayer of 2-dimensional (2D) nanosheets provides new and intriguing confined environments for molecular interactions. However, atomic level understanding of the adsorption mechanism of CO

Accurate virial coefficients BN(λ,ε) (where ε is the well depth) for the three-dimensional square-well and square-step potentials are calculated for orders N = 5–9 and well widths λ = 1.1−2.0 using a very fast recursive method. The efficiency of the algorithm is enhanced significantly by exploiting permutation symmetry and by storing integrands for reuse during the calculation. For N = 9 the storage requirements become sufficiently large that a parallel algorithm is developed. The methodology is general and is applicable to other discrete potentials. The computed coefficients are precise even near the critical temperature, and thus open up possibilities for analysis of criticality of the system, which is currently not accessible by any other means.

It is challenging to compute the partition function (Q) for systems with enormous configurational spaces, such as fluids. Recently, we developed a Monte Carlo technique (an energy partitioning method) for computing Q [ J. Chem. Phys. 2011 , 135 , 174105 ]. In this paper, we use this approach to compute the partition function of a binary fluid mixture (carbon dioxide + methane); this allows us to obtain the Helmholtz free energy (F) via F = -k(B)T ln Q and the Gibbs free energy (G) via G = F + pV. We then utilize G to obtain the coexisting mole fraction curves. The chemical potential of each species is also obtained. At the vapor-liquid equilibrium condition, the chemical potential of methane significantly increases, while that of carbon dioxide slightly decreases, as the pressure increases along an isotherm. Since Q is obtained from the density of states, which is independent of the temperature, equilibrium thermodynamic properties at any condition can be obtained by varying the total composition and volume of the system. Our methodology can be adapted to explore the free energies of other binary mixtures in general and of those containing CO(2) in particular. Since the method gives access to the free energy and chemical potentials, it will be useful in many other applications.

We present ab initio calculations on the CH4–CH4 and CH4–CO2 dimer potential energy surfaces. We show that the fit to these surfaces is improved over the Lennard–Jones potential by changing the form of the repulsive wall. Ab initio calculations are also performed on trimers to evaluate the strength of nonadditive interactions. The experimental CH4 phase properties are reproduced in simulations that include correction for nonadditive dispersion. The phase-coexistence curve of mixtures of CH4 and CO2 is also improved by including this nonadditive dispersion term.

We propose a new simulation method, which combines a cage model and a density of states partitioning technique, to compute the free energy of an arbitrary solid. The excess free energy is separated into two contributions, noninteracting and interacting. The excess free energy of the noninteracting solid is computed by partitioning its geometrical configuration space with respect to the ideal gas. This quantity depends on the lattice type and the number of molecules. The excess free energy of the interacting solid, with respect to the noninteracting solid, is calculated using density of states partitioning and a cage model. The cage model is better than the cell model in that it has a smaller configuration space and better represents the equilibrium distribution of solid configurations. Since the partition function (and hence free energy) is obtained from the density of states, which is independent of the temperature, equilibrium thermodynamic properties at any condition can be obtained by varying the density. We illustrate our method in the context of the free energy of dry ice.

A rapid method to parameterize the intramolecular component of classical force fields for complex conjugated molecules is proposed. The method is based on a procedure of force matching with a reference electronic structure calculation. It is particularly suitable for those applications where molecular dynamics simulations are used to generate structures that are therefore analysed by electronic structure methods, because it is possible to build force fields that are consistent with electronic structure calculations that follow classical simulations. Such applications are commonly encountered in organic electronics, spectroscopy of complex systems and photobiology (e.g. photosynthetic systems). We illustrate the method by parameterizing the force fields of a molecule used in molecular semiconductors (2,2-dicyanovinyl-capped S,N-heteropentacene or DCV-SN5), a polymeric semiconductor (thieno[3,2-b]thiophene-diketopyrrolopyrrole TT-DPP) and a chromophore embedded in a protein environment (15,16-dihydrobiliverdin or DBV) where several hundreds of parameters need to be optimized in parallel.

© the Owner Societies 2015. Vibrational frequencies for carbon clusters, fullerenes and nanotubes evaluated using empirical carbon-carbon potentials are presented. For linear and cyclic clusters, frequencies evaluated with the reactive empirical bond order (REBO) potential provide the closest agreement with experiment. The mean absolute deviation (MAD) between experiment and the calculated harmonic frequencies is 79 cm-1 for the bending modes and 76 cm-1 for the stretching modes. The effects of anharmonicity are included via second order vibrational perturbation theory and tend to increase the frequency of the bending modes while the stretching modes have negative shifts in the region of 20-60 cm-1, with larger shifts for the higher frequency modes. This results in MADs for the bending and stretching modes of 84 cm-1 and 58 cm-1, respectively. For the fullerene molecule C60, the high frequency modes are predicted to have harmonic frequencies that are significantly higher than experiment, and this is not corrected by accounting for anharmonicity. This overestimation of experimental observed frequencies is also evident in the calculated frequencies of the G band in nanotubes. This suggests that the REBO potential is not optimal for these larger systems and it is shown that adjustment of the parameters within the potential leads to closer agreement with experiment, particularly if higher and lower frequency modes are considered separately.

International audience; A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Moller-Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr-2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.

The calculation of the electronic circular dichroism (CD) spectra of the oxidised form of the blue copper proteins plastocyanin and cucumber basic protein and the relationship between the observed spectral features and the structure of the active site of the protein is investigated. Excitation energies and transition strengths are computed using multi reference configuration interaction, and it is shown that computed spectra based on coordinates from the crystal structure or a single structure optimised in quantum mechanics/molecular mechanics (QM/MM) or ligand field molecular mechanics (LFMM) are qualitatively incorrect. In particular, the rotational strength of the ligand to metal charge transfer band is predicted to be too small or have the incorrect sign. By considering calculations on active site models with modified structures it is shown that the intensity of this band is sensitive to the non-planarity of the histidine and cysteine ligands coordinated to copper. Calculation of the ultraviolet absorption and CD spectra based upon averaging over many structures drawn from a LFMM molecular dynamics simulation are in good agreement with experiment, and superior to analogous calculations based upon structures from a classical molecular dynamics simulation. This provides evidence that the LFMM force field provides an accurate description of the molecular dynamics of these proteins.

The structure and bonding in ionized water clusters, (H2O)(n)(+) (n = 3–9), has been studied using the basin hopping search algorithm in combination with quantum chemical calculations. Initially candidate low energy isomers were generated using basin hopping in conjunction with density functional theory. Subsequently, the structures and energies were refined using second order Møller–Plesset perturbation theory and coupled cluster theory, respectively. The lowest energy isomers are found to involve proton transfer to give H(3)O(+) and a OH radical, which are more stable than isomers containing the hemibonded hydrazine-like fragment (H(2)O–OH(2)), with the calculated infrared spectra consistent with experimental data. For (H(2)O)(9)(+) the observation of a new structural motif comprising proton transfer to form H(3)O(+) and OH, but with the OH radical involved in hemibonding to another water molecule is discussed.

A robust and model free Monte Carlo simulation method is proposed to address the challenge in computing the classical density of states and partition function of solids. Starting from the minimum configurational energy, the algorithm partitions the entire energy range in the increasing energy direction ("upward") into subdivisions whose integrated density of states is known. When combined with the density of states computed from the "downward" energy partitioning approach [H. Do, J. D. Hirst, and R. J. Wheatley, J. Chem. Phys. 135, 174105 (2011)], the equilibrium thermodynamic properties can be evaluated at any temperature and in any phase. The method is illustrated in the context of the Lennard-Jones system and can readily be extended to other molecular systems and clusters for which the structures are known.

The copper-sulfur bond that binds cysteinate to the metal center is a key factor in the spectroscopy of blue copper proteins. We present theoretical calculations describing the electronically excited states of small molecules, including CuSH, CuSCH(3), (CH(3))(2)SCuSH, (imidazole)-CuSH, and (imidazole)(2)-CuSH, derived from the active site of blue copper proteins that contain the copper-sulfur bond in order to identify small molecular systems that have electronic structure that is analogous to the active site of the proteins. Both neutral and cationic forms are studied since these represent the reduced and oxidized forms of the protein, respectively. For CuSH and CuSH(+), excitation energies from time-dependent density functional theory with the B97-1 exchange-correlation functional agree well with the available experimental data and multireference configuration interaction calculations. For the positive ions, the singly occupied molecular orbital is formed from an antibonding combination of a 3d orbital on copper and a 3p(π) orbital on sulfur, which is analogous to the protein. This leads several of the molecules to have qualitatively similar electronic spectra to the proteins. For the neutral molecules, changes in the nature of the low lying virtual orbitals leads the predicted electronic spectra to vary substantially between the different molecules. In particular, addition of a ligand bonded directly to copper results in the low-lying excited states observed in CuSH and CuSCH(3) to be absent or shifted to higher energies.

Gibbs ensemble Monte Carlo simulations were used to study the vapor-liquid equilibrium of binary mixtures of carbon dioxide + methane and carbon dioxide + difluoromethane. The potential forcefields we employ are all atomistic models, and have not previously been mixed together to study the vapor-liquid equilibrium of the binary mixtures. In addition, we characterize the microscopic structure of these liquid mixtures. In carbon dioxide + methane at 230 K and 56 bar, the microscopic structure of carbon dioxide in the mixture is the same as that in the pure liquid. In carbon dioxide + difluoromethane at 283 K and 56 bar, the presence of carbon dioxide does not noticeably perturb the liquid structure of difluoromethane, but the structure of carbon dioxide is subtly changed, due to a strong interaction between it and difluoromethane. The simulations in the isobaric-isothermal (NPT) ensemble agree well with the experimental data, except at the two extreme regions of the pressure range. The good agreement of most simulated state points with experimental data encourages one to develop more accurate potentials for predicting the thermodynamic properties of these systems as well as other complicated systems, which are less amenable to measurement by experiment.

The basin hopping search algorithm in conjunction with second-order Møller-Plesset perturbation theory is used to determine the lowest energy structures of the radical cation clusters (NH3)n˙(+), (H2O)n˙(+), (HF)n˙(+), (PH3)n˙(+), (H2S)n˙(+) and (HCl)n˙(+), where n = 2-4. The energies of the most stable structures are subsequently evaluated using coupled cluster theory in conjunction with the aug-cc-pVTZ basis set. These cationic clusters can adopt two distinct structural types, with some clusters showing an unusual type of bonding, often referred to as hemibonding, while other clusters undergo proton transfer to give an ion and radical. It is found that proton transfer based structures are preferred by the (NH3)n˙(+), (H2O)n˙(+) and (HF)n˙(+) clusters while hemibonded structures are favoured by (PH3)n˙(+), (H2S)n˙(+) and (HCl)n˙(+). These trends can be attributed to the relative strengths of the molecules and molecular cations as Brønsted bases and acids, respectively, and the strength of the interaction between the ion and radical in the ion-radical clusters.

The partition function (Q) is a central quantity in statistical mechanics. All the thermodynamic properties can be derived from it. Here we show how the partition function of fluids can be calculated directly from simulations; this allows us to obtain the Helmholtz free energy (F) via F = -k(B)T ln Q. In our approach, we divide the density of states, assigning half of the configurations found in a simulation to a high-energy partition and half to a low-energy partition. By recursively dividing the low-energy partition into halves, we map out the complete density of states for a continuous system. The result allows free energy to be calculated directly as a function of temperature. We illustrate our method in the context of the free energy of water.

We present pair potentials for fluorinated methanes and their dimers with CO(2) based on ab initio potential energy surfaces. These potentials reproduce the experimental second virial coefficients of the pure fluorinated methanes and their mixtures with CO(2) without adjustment. Ab initio calculations on trimers are used to model the effects of nonadditive dispersion and induction. Simulations using these potentials reproduce the experimental phase-coexistence properties of CH(3)F within 10% over a wide range of temperatures. The phase coexistence curve of the mixture of CH(2)F(2) and CO(2) is reproduced with an error in the mole fractions of both phases of less than 0.1. The potentials described here are based entirely on ab initio calculations, with no empirical fits to improve the agreement with experiment.

The refrigerant 1-1-1-2-tetrafluoroethane (R134a) is being phased out in Europe from 2011. This requires the adoption of alternatives, and the mixture of R134a with carbon dioxide (CO(2)) is a promising candidate. However, limited experimental data currently stymie evaluation of its performance in industrial applications. In this paper, we employ atomistic force fields and the configurational-bias Monte Carlo technique to study the vapour-liquid equilibrium of this mixture. We also characterize the microscopic structure of the mixture, which is not readily available from experiments. At 272 K and 11.55 bar, the average coordination number of the first solvation shell of R134a is 11 and that of CO(2) is eight. CO(2) does not alter the structure of R134a, but its structure is slightly changed, due to the presence of R134a. All pair interactions are sensitive to pressure and are more structured at lower pressure. CO(2) prefers to form clusters of two in the mixture and highly extended or percolating clusters are not found.

1-1-1-2-tetrafluoroethane (R134a) is one of the most commonly used refrigerants. Its thermophysical properties are important for evaluating the performance of refrigeration cycles. These can be obtained via computer simulation, with an insight into the microscopic structure of the liquid, which is not accessible to experiment. In this paper, vapour–liquid equilibrium properties of R134a and its liquid microscopic structure are investigated using coupled–decoupled configurational-bias Monte Carlo simulation in the Gibbs ensemble, with a recent potential [J. Phys. Chem. B 2009, 113, 178]. We find that the simulations agree well with the experimental data, except at the vicinity of the critical region. Liquid R134a packs like liquid argon, with a coordination number in the first solvation shell of 12 at 260 K. The nearest neighbours prefer to be localized in three different spaces around the central molecule, in such a manner that the dipole moments are in a parallel alignment. Analysis of the pair interaction energy shows clear association of R134a molecules, but no evidence for C–H⋯F type hydrogen bonding is found. The above findings should be of relevance to a broad range of fluoroalkanes.

Identifying the energy minima of molecular clusters is a challenging problem. Traditionally, search algorithms such as simulated annealing, genetic algorithms, or basin hopping are usually used in conjunction with empirical force fields. We have implemented a basin hopping search algorithm combined with density functional theory to enable the optimization of molecular clusters without the need for empirical force fields. This approach can be applied to systems where empirical potentials are not available or may not be sufficiently accurate. We illustrate the effectiveness of the method with studies on water, methanol, and water + methanol clusters as well as protonated water and methanol clusters at the B3LYP+D/6-31+G* level of theory. A new lowest energy structure for H(+)(H(2)O)(7) is predicted at the B3LYP+D/6-31+G* level. In all of the protonated mixed water and methanol clusters, we find that H(+) prefers to combine with methanol rather than water in the lowest-energy structures.