Physical Chemistry Chemical Physics

Goli, Mohammad;Shahbazian, Shant

doi: 10.1039/C8CP02489Hpmid: 29881845

Abstract: Recently we have proposed an effective Hartree-Fock (EHF) theory for the electrons of the muonic molecules that is formally equivalent to the HF theory within the context of the Nuclear-Electronic Orbital theory [Phys. Chem. Chem. Phys. 20, 4466 (2018)]. In the present report we extend the muon-specific effective electronic structure theory beyond the EHF level by introducing the effective second order Muller-Plesset perturbation theory (EMP2) and the effective coupled-cluster theory at single and double excitation levels (ECCSD) as well as an improved version including perturbative triple excitations (ECCSD(T)). These theories incorporate electron-electron correlation into the effective paradigm and through their computational implementation, a diverse set of small muonic species is considered as a benchmark at these post-EHF levels. A comparative computational study on this set demonstrates that the muonic bond length is in general non-negligibly longer than corresponding hydrogenic analogs. Next, the developed post-EHF theories are applied for the muoniated N-Heterocyclic carbene/silylene/germylene and the muoniated triazolium cation revealing the relative stability of the sticking sites of the muon in each species. The computational results, in line with previously reported experimental data demonstrate that the muon generally prefers to attach to the divalent atom with carbeneic nature. A detailed comparison of these muonic adducts with the corresponding hydrogenic adducts reveals subtle differences that have already been overlooked.

Jain, Sandeep K.;Barkema, Gerard T.

doi: 10.1039/C8CP01960Fpmid: 29897061

Abstract: Apart from its unique and exciting electronic properties, many sensor based applications of graphene are purely based on its mechanical and structural properties. Here we report a numerical and analytical study of a void in amorphous (small domain polycrystalline) graphene, and show that the energetics of a void is a balance between the line tension cost versus the increased area gain. Using the concepts of classical nucleation theory, we show that the critical radius of a void formed in amorphous graphene at constant pressure is simply the ratio of line tension at the void and the applied pressure. The values of the critical radius of the void for flat and buckled graphene are 3.48Å~and 3.31Å, respectively at 2 eV/Å${^2}$ pressure. We also show that the dominant finite size correction to the line tension is inversely proportional to the radius of the void in both flat and buckled cases. Contrary to conventional wisdom, with the help of a simple analytical model we find that the shear modulus sets the lower limit of the line tension in the samples. This makes our study relevant for other two-dimensional amorphous materials such as h-BN, phosphorene, borophene, and transition metal dichalcogenides. Our results are useful for the better understanding of polycrystalline graphene under tension and therefore have direct implications on the very fascinating field of strain engineering known as "straintronics" to manipulate or improve graphene's properties.

Laurati, Marco;Sentjabrskaja, Tatjana;Ruiz-Franco, José;Egelhaaf, Stefan U.;Zaccarelli, Emanuela

doi: 10.1039/C8CP02559Bpmid: 29955749

Abstract: Colloidal mixtures represent a versatile model system to study transport in complex environments. They allow for a systematic variation of the control parameters, namely size ratio, total volume fraction and composition. We study the effects of these parameters on the dynamics of dense suspensions using molecular dynamics simulations and differential dynamic microscopy experiments. We investigate the motion of the small particles through the matrix of large particles as well as the motion of the large particles. A particular focus is on the coupling of the collective dynamics of the small and large particles and on the different mechanisms leading to this coupling. For large size ratios, about 1:5, and an increasing fraction of small particles, the dynamics of the two species become increasingly coupled and reflect the structure of the large particles. This is attributed to the dominant effect of the large particles on the motion of the small particles which is mediated by the increasing crowding of the small particles. Furthermore, for moderate size ratios, about 1:3, and sufficiently high fractions of small particles, mixed cages are formed and hence the dynamics are also strongly coupled. Again, the coupling becomes weaker as the fraction of small particles is decreased. In this case, however, the collective intermediate scattering function of the small particles shows a logarithmic decay corresponding to a broad range of relaxation times.

Sopiha, Kostiantyn V.;Malyi, Oleksandr I.;Persson, Clas;Wu, Ping

doi: 10.1039/C8CP02535Epmid: 29964284

Abstract: By using first-principles approach, the interaction of CO${_2}$ with (001) surfaces of six cubic ABO${_3}$ perovskites (A = Ba, Sr and B = Ti, Zr, Hf) is studied in detail. We show that CO${_2}$ adsorption results in the formation of highly stable CO${_3}$-like complexes with similar geometries for all investigated compounds. This reaction leads to the suppression of the surfaces states, opening the band gaps of the slab systems up to the corresponding bulk energy limits. For most AO-terminated ABO${_3}$(001) perovskite surfaces, a CO${_2}$ coverage of 0.25 was found to be sufficient to fully suppress the surface states, whereas the same effect can only be achieved at 0.50 CO${_2}$ coverage for the BO${_2}$ terminations. The largest band gap modulation among the AO-terminated surfaces was found for SrHfO${_3}$(001) and BaHfO${_3}$(001), whereas the most profound effect among the BO${_2}$ terminations was identified for SrTiO${_3}$(001) and BaTiO${_3}$(001). Based on these results and considering practical difficulties associated with measuring conductivity of highly resistive materials, TiO${_2}$-terminated SrTiO${_3}$(001) and BaTiO${_3}$(001) were identified as the most prospective candidates for chemiresistive CO${_2}$ sensing applications.

Gutić, Sanjin J.;Kozlica, Dževad;Korać, Fehim;Bajuk-Bogdanović, Danica;Mitrić, Miodrag;Mirsky, Vladimir M.;Mentus, Slavko V.;Pašti, Igor A.

doi: 10.1039/C8CP03631Dpmid: 30137091

Abstract: Increasing energy demands of modern society requires deep understanding of the properties of energy storage materials as well as their performance tuning. We show that the capacitance of graphene oxide (GO) can be precisely tuned using a simple electrochemical reduction route. In situ resistance measurements, combined with cyclic voltammetry measurement and Raman spectroscopy, have shown that upon the reduction GO is irreversibly deoxygenated which is further accompanied with structural ordering and increasing of electrical conductivity. The capacitance is maximized when the concentration of oxygen functional groups is properly balanced with the conductivity. Any further reduction and de-oxygenation leads to the gradual loss of the capacitance. The observed trend is independent on the preparation route and on the exact chemical and structural properties of GO. It is proposed that an improvement of capacitive properties of any GO can be achieved by optimization of its reduction conditions.

Chaban, Vitaly V.

doi: 10.1039/C8CP04012Epmid: 30198535

Abstract: Senior dialkyl sulfoxides constitute interest in the context of biomedical sciences due to their abilities to penetrate phospholipid bilayers, dissolve drugs, and serve as cryoprotectants. Intermolecular interactions with water, a paramount component of the living cell, determine performance the sulfoxide-based artificial systems in their prospective applications. Herein, we simulated a wide composition range of the sulfoxide/water mixtures, up to 85 w/w% sulfoxide using classical molecular dynamics to determine structure, dynamics, and thermodynamics as a function of the mixture composition. As found, both diethyl sulfoxide (DESO) and ethyl methyl sulfoxide (EMSO) are strongly miscible with water. DESO and EMSO based aqueous mixtures exhibit similar structure and thermodynamic properties, however, quite different dynamic properties over an entire range of compositions. Strong deviations from an ideal mixture between 30 50 mol% of sulfoxide content leads to relatively high shear viscosities of the mixtures. Free energy of mixing with water is only slightly more favorable for EMSO than for DESO. The results, for the first time, quantify high miscibilities of both sulfoxides with water and motivate comprehensive in vivo investigation of the proposed mixtures.

Mádai, Eszter;Matejczyk, Bartłomiej;Dallos, András;Valiskó, Mónika;Boda, Dezső

doi: 10.1039/C8CP03918Fpmid: 30206599

Abstract: We present a modeling study of a nanopore-based transistor computed by a mean-field continuum theory (Poisson-Nernst-Planck, PNP) and a hybrid method including particle simulation (Local Equilibrium Monte Carlo, LEMC) that is able to take ionic correlations into account including finite size of ions. The model is composed of three regions along the pore axis with the left and right regions determining the ionic species that is the main charge carrier, and the central region tuning the concentration of that species and, thus, the current flowing through the nanopore. We consider a model of small dimensions with the pore radius comparable to the Debye-screening length ($R_{\mathrm{pore}}/\lambda_{\mathrm{D}}\approx 1$), which, together with large surface charges provides a mechanism for creating depletion zones and, thus, controlling ionic current through the device. We report scaling behavior of the device as a function the $R_{\mathrm{pore}}/\lambda_{\mathrm{D}}$ parameter. Qualitative agreement between PNP and LEMC results indicates that mean-field electrostatic effects determine device behavior to the first order.

Dong, Haikuan;Hirvonen, Petri;Fan, Zheyong;Ala-Nissila, Tapio

doi: 10.1039/C8CP05159Cpmid: 30229758

Abstract: We use a phase field crystal model to generate large-scale bicrystalline and polycrystalline single-layer hexagonal boron nitride (h-BN) samples and employ molecular dynamics (MD) simulations with the Tersoff many-body potential to study their heat transport properties. The Kapitza thermal resistance across individual h-BN grain boundaries is calculated using the inhomogeneous nonequilibrium MD method. The resistance displays strong dependence on the tilt angle, the line tension and the defect density of the grain boundaries. We also calculate the thermal conductivity of pristine h-BN and polycrystalline h-BN with different grain sizes using an efficient homogeneous nonequilibrium MD method. The in-plane and the out-of-plane (flexural) phonons exhibit different grain size scalings of the thermal conductivity in polycrystalline h-BN and the extracted Kapitza conductance is close to that of large-tilt-angle grain boundaries in bicrystals.

Matsko, N. L.

doi: 10.1039/C8CP04521Fpmid: 30238107

Abstract: Numerical calculations of surface and volume plasma excitations in silicon and silicon-hydrogen nanoclusters in the range Si$_{10}$-Si$_{60}$ and Si$_3$H$_8$-Si$_{39}$H$_{40}$ are performed. Some nanocluster structures were obtained using the evolutionary algorithm, others were taken from the database. The GW method was used to calculate the response function and self-energy of the structures under study. The applied method shows the results consistent with the experiment (except plasmaron artifacts) and sufficient sensitivity allowing to investigate the effect of the cluster structure and size on the specific properties of plasma excitations. In the studied silicon and silicon-hydrogen nanoclusters the surface is one of the key factors affecting the properties of the plasmons. Passivation of silicon dangling bonds on cluster surface changes frequency of plasmons and significantly decreases their damping. It makes the surface and volume plasmons to be clearly distinguishable even in small clusters.

Kahk, J. Matthias;Lischner, Johannes

doi: 10.1039/C8CP04955Fpmid: 30499572

Abstract: Core-level X-ray Photoelectron Spectroscopy (XPS) is often used to study the surfaces of heterogeneous copper-based catalysts, but the interpretation of measured spectra, in particular the assignment of peaks to adsorbed species, can be extremely challenging. In this study we demonstrate that first principles calculations using the delta Self Consistent Field (delta-SCF) method can be used to guide the analysis of experimental core-level spectra of complex surfaces relevant to heterogeneous catalysis. Specifically, we calculate core-level binding energy shifts for a series of adsorbates on Cu(111) and show that the resulting C1s and O1s binding energy shifts for adsorbed CO, CO2, C2H4, HCOO, CH3O, H2O, OH and a surface oxide on Cu(111) are in good overall agreement with the experimental literature. In the few cases where the agreement is less good, the theoretical results may indicate the need to re-examine experimental peak assignments.