@article{9666, abstract = {Predicting phase stabilities of crystal polymorphs is central to computational materials science and chemistry. Such predictions are challenging because they first require searching for potential energy minima and then performing arduous free-energy calculations to account for entropic effects at finite temperatures. Here, we develop a framework that facilitates such predictions by exploiting all the information obtained from random searches of crystal structures. This framework combines automated clustering, classification and visualisation of crystal structures with machine-learning estimation of their enthalpy and entropy. We demonstrate the framework on the technologically important system of TiO2, which has many polymorphs, without relying on prior knowledge of known phases. We find a number of new phases and predict the phase diagram and metastabilities of crystal polymorphs at 1600 K, benchmarking the results against full free-energy calculations.}, author = {Reinhardt, Aleks and Pickard, Chris J. and Cheng, Bingqing}, issn = {1463-9084}, journal = {Physical Chemistry Chemical Physics}, number = {22}, pages = {12697--12705}, publisher = {Royal Society of Chemistry}, title = {{Predicting the phase diagram of titanium dioxide with random search and pattern recognition}}, doi = {10.1039/d0cp02513e}, volume = {22}, year = {2020}, } @article{9668, abstract = {Estimating the homogeneous ice nucleation rate from undercooled liquid water is crucial for understanding many important physical phenomena and technological applications, and challenging for both experiments and theory. From a theoretical point of view, difficulties arise due to the long time scales required, as well as the numerous nucleation pathways involved to form ice nuclei with different stacking disorders. We computed the homogeneous ice nucleation rate at a physically relevant undercooling for a single-site water model, taking into account the diffuse nature of ice–water interfaces, stacking disorders in ice nuclei, and the addition rate of particles to the critical nucleus. We disentangled and investigated the relative importance of all the terms, including interfacial free energy, entropic contributions and the kinetic prefactor, that contribute to the overall nucleation rate. Breaking down the problem into pieces not only provides physical insights into ice nucleation, but also sheds light on the long-standing discrepancy between different theoretical predictions, as well as between theoretical and experimental determinations of the nucleation rate. Moreover, we pinpoint the main shortcomings and suggest strategies to systematically improve the existing simulation methods.}, author = {Cheng, Bingqing and Dellago, Christoph and Ceriotti, Michele}, issn = {1463-9084}, journal = {Physical Chemistry Chemical Physics}, number = {45}, pages = {28732--28740}, publisher = {Royal Society of Chemistry}, title = {{Theoretical prediction of the homogeneous ice nucleation rate: Disentangling thermodynamics and kinetics}}, doi = {10.1039/c8cp04561e}, volume = {20}, year = {2018}, } @article{17964, abstract = {Charge transfer rates at metal/organic interfaces affect the efficiencies of devices for organic based electronics and photovoltaics. A quantitative study of electron transfer rates, which take place on the femtosecond timescale, is often difficult, especially since in most systems the molecular adsorption geometry is unknown. Here, we use X-ray resonant photoemission spectroscopy to measure ultrafast charge transfer rates across pyridine/Au(111) interfaces while also controlling the molecular orientation on the metal. We demonstrate that a bi-directional charge transfer across the molecule/metal interface is enabled upon creation of a core-exciton on the molecule with a rate that has a strong dependence on the molecular adsorption angle. Through density functional theory calculations, we show that the alignment of molecular levels relative to the metal Fermi level is dramatically altered when a core-hole is created on the molecule, allowing the lowest unoccupied molecular orbital to fall partially below the metal Fermi level. We also calculate charge transfer rates as a function of molecular adsorption geometry and find a trend that agrees with the experiment. These findings thus give insight into the charge transfer dynamics of a photo-excited molecule on a metal surface.}, author = {Cvetko, Dean and Fratesi, Guido and Kladnik, Gregor and Cossaro, Albano and Brivio, Gian Paolo and Venkataraman, Latha and Morgante, Alberto}, issn = {1463-9084}, journal = {Physical Chemistry Chemical Physics}, number = {32}, pages = {22140--22145}, publisher = {Royal Society of Chemistry}, title = {{Ultrafast electron injection into photo-excited organic molecules}}, doi = {10.1039/c6cp04099c}, volume = {18}, year = {2016}, } @article{18004, abstract = {We characterize electron transport across Au–molecule–Au junctions of heterogeneous carboxyl and methyl sulfide terminated saturated and conjugated molecules. Low-bias conductance measurements are performed using the scanning tunneling microscopy based break-junction technique in the presence of solvents and at room temperature. For a series of alkanes with 1–4 carbon atoms in the hydrocarbon chain, our results show an exponential decrease in conductance with increasing molecule length characterized by a decay constant of 0.9 ± 0.1 per methylene group. Control measurements in pH 11 solutions and with COOMe terminations suggest that the carboxylic acid group binds through the formation of a COO−–Au bond. Simultaneous measurements of conductance and force across these junctions yield a rupture force of 0.6 ± 0.1 nN, comparable to that required to rupture a Au–SMe bond. By establishing reliable, in situ junction formation, these experiments provide a new approach to probe electronic properties of carboxyl groups at the single molecule level.}, author = {Ahn, Seokhoon and Aradhya, Sriharsha V. and Klausen, Rebekka S. and Capozzi, Brian and Roy, Xavier and Steigerwald, Michael L. and Nuckolls, Colin and Venkataraman, Latha}, issn = {1463-9084}, journal = {Physical Chemistry Chemical Physics}, number = {40}, publisher = {Royal Society of Chemistry}, title = {{Electronic transport and mechanical stability of carboxyl linked single-molecule junctions}}, doi = {10.1039/c2cp41578j}, volume = {14}, year = {2012}, }