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1.
Inorg Chem ; 58(22): 14939-14980, 2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-31668070

RESUMO

Nanostructured materials are essential building blocks for the fabrication of new devices for energy harvesting/storage, sensing, catalysis, magnetic, and optoelectronic applications. However, because of the increase of technological needs, it is essential to identify new functional materials and improve the properties of existing ones. The objective of this Viewpoint is to examine the state of the art of atomic-scale simulative and experimental protocols aimed to the design of novel functional nanostructured materials, and to present new perspectives in the relative fields. This is the result of the debates of Symposium I "Atomic-scale design protocols towards energy, electronic, catalysis, and sensing applications", which took place within the 2018 European Materials Research Society fall meeting.

2.
Sci Adv ; 5(2): eaav0693, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30783625

RESUMO

Predicting the stability of the perovskite structure remains a long-standing challenge for the discovery of new functional materials for many applications including photovoltaics and electrocatalysts. We developed an accurate, physically interpretable, and one-dimensional tolerance factor, τ, that correctly predicts 92% of compounds as perovskite or nonperovskite for an experimental dataset of 576 ABX 3 materials (X = O2-, F-, Cl-, Br-, I-) using a novel data analytics approach based on SISSO (sure independence screening and sparsifying operator). τ is shown to generalize outside the training set for 1034 experimentally realized single and double perovskites (91% accuracy) and is applied to identify 23,314 new double perovskites (A 2 BB'X 6) ranked by their probability of being stable as perovskite. This work guides experimentalists and theorists toward which perovskites are most likely to be successfully synthesized and demonstrates an approach to descriptor identification that can be extended to arbitrary applications beyond perovskite stability predictions.

3.
J Phys Chem Lett ; 10(3): 685-692, 2019 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-30681851

RESUMO

Gold nanoclusters have been the focus of numerous computational studies, but an atomistic understanding of their structural and dynamical properties at finite temperature is far from satisfactory. To address this deficiency, we investigate gold nanoclusters via ab initio molecular dynamics, in a range of sizes where a core-shell morphology is observed. We analyze their structure and dynamics using state-of-the-art techniques, including unsupervised machine-learning nonlinear dimensionality reduction (sketch-map) for describing the similarities and differences among the range of sampled configurations. In the examined temperature range between 300 and 600 K, we find that whereas the gold nanoclusters exhibit continuous structural rearrangement, they are not amorphous. Instead, they clearly show persistent motifs: a cationic core of 1-5 atoms is loosely bound to a shell which typically displays a substructure resulting from the competition between locally spherical versus planar fragments. Besides illuminating the properties of core-shell gold nanoclusters, the present study proposes a set of useful tools for understanding their nature in operando.

4.
Nat Commun ; 9(1): 2775, 2018 07 17.
Artigo em Inglês | MEDLINE | ID: mdl-30018362

RESUMO

Computational methods that automatically extract knowledge from data are critical for enabling data-driven materials science. A reliable identification of lattice symmetry is a crucial first step for materials characterization and analytics. Current methods require a user-specified threshold, and are unable to detect average symmetries for defective structures. Here, we propose a machine learning-based approach to automatically classify structures by crystal symmetry. First, we represent crystals by calculating a diffraction image, then construct a deep learning neural network model for classification. Our approach is able to correctly classify a dataset comprising more than 100,000 simulated crystal structures, including heavily defective ones. The internal operations of the neural network are unraveled through attentive response maps, demonstrating that it uses the same landmarks a materials scientist would use, although never explicitly instructed to do so. Our study paves the way for crystal structure recognition of-possibly noisy and incomplete-three-dimensional structural data in big-data materials science.

5.
J Chem Theory Comput ; 14(4): 2246-2264, 2018 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-29481740

RESUMO

We present the implementation of GAtor, a massively parallel, first-principles genetic algorithm (GA) for molecular crystal structure prediction. GAtor is written in Python and currently interfaces with the FHI-aims code to perform local optimizations and energy evaluations using dispersion-inclusive density functional theory (DFT). GAtor offers a variety of fitness evaluation, selection, crossover, and mutation schemes. Breeding operators designed specifically for molecular crystals provide a balance between exploration and exploitation. Evolutionary niching is implemented in GAtor by using machine learning to cluster the dynamically updated population by structural similarity and then employing a cluster-based fitness function. Evolutionary niching promotes uniform sampling of the potential energy surface by evolving several subpopulations, which helps overcome initial pool biases and selection biases (genetic drift). The various settings offered by GAtor increase the likelihood of locating numerous low-energy minima, including those located in disconnected, hard to reach regions of the potential energy landscape. The best structures generated are re-relaxed and re-ranked using a hierarchy of increasingly accurate DFT functionals and dispersion methods. GAtor is applied to a chemically diverse set of four past blind test targets, characterized by different types of intermolecular interactions. The experimentally observed structures and other low-energy structures are found for all four targets. In particular, for Target II, 5-cyano-3-hydroxythiophene, the top ranked putative crystal structure is a Z' = 2 structure with P1̅ symmetry and a scaffold packing motif, which has not been reported previously.

6.
Acta Crystallogr B Struct Sci Cryst Eng Mater ; 72(Pt 4): 439-59, 2016 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-27484368

RESUMO

The sixth blind test of organic crystal structure prediction (CSP) methods has been held, with five target systems: a small nearly rigid molecule, a polymorphic former drug candidate, a chloride salt hydrate, a co-crystal and a bulky flexible molecule. This blind test has seen substantial growth in the number of participants, with the broad range of prediction methods giving a unique insight into the state of the art in the field. Significant progress has been seen in treating flexible molecules, usage of hierarchical approaches to ranking structures, the application of density-functional approximations, and the establishment of new workflows and `best practices' for performing CSP calculations. All of the targets, apart from a single potentially disordered Z' = 2 polymorph of the drug candidate, were predicted by at least one submission. Despite many remaining challenges, it is clear that CSP methods are becoming more applicable to a wider range of real systems, including salts, hydrates and larger flexible molecules. The results also highlight the potential for CSP calculations to complement and augment experimental studies of organic solid forms.

7.
J Phys Chem Lett ; 6(7): 1204-8, 2015 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-26262972

RESUMO

Formation of partly dissociated water chains is observed on CaO(001) films upon water exposure at 300 K. While morphology and orientation of the 1D assemblies are revealed from scanning tunneling microscopy, their atomic structure is identified with infrared absorption spectroscopy combined with density functional theory calculations. The latter exploit an ab initio genetic algorithm linked to atomistic thermodynamics to determine low-energy H2O configurations on the oxide surface. The development of 1D structures on the C4v symmetric CaO(001) is triggered by symmetry-broken water tetramers and a favorable balance between adsorbate-adsorbate versus adsorbate-surface interactions at the constraint of the CaO lattice parameter.

8.
Phys Rev Lett ; 114(10): 105503, 2015 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-25815947

RESUMO

Statistical learning of materials properties or functions so far starts with a largely silent, nonchallenged step: the choice of the set of descriptive parameters (termed descriptor). However, when the scientific connection between the descriptor and the actuating mechanisms is unclear, the causality of the learned descriptor-property relation is uncertain. Thus, a trustful prediction of new promising materials, identification of anomalies, and scientific advancement are doubtful. We analyze this issue and define requirements for a suitable descriptor. For a classic example, the energy difference of zinc blende or wurtzite and rocksalt semiconductors, we demonstrate how a meaningful descriptor can be found systematically.

9.
Phys Rev Lett ; 111(13): 135501, 2013 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-24116790

RESUMO

By applying a genetic algorithm and ab initio atomistic thermodynamics, we identify the stable and metastable compositions and structures of MgMOx clusters at realistic temperatures and oxygen pressures. We find that small clusters (M≲5) are in thermodynamic equilibrium when x>M. The nonstoichiometric clusters exhibit peculiar magnetic behavior, suggesting the possibility of tuning magnetic properties by changing environmental pressure and temperature conditions. Furthermore, we show that density-functional theory with a hybrid exchange-correlation functional is needed for predicting accurate phase diagrams of metal-oxide clusters. Neither a (sophisticated) force field nor density-functional theory with (semi)local exchange-correlation functionals is sufficient for even a qualitative prediction.

10.
J Am Chem Soc ; 134(46): 19217-22, 2012 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-23098232

RESUMO

Water-metal interfaces are ubiquitous and play a key role in many chemical processes, from catalysis to corrosion. Whereas water adlayers on atomically flat transition metal surfaces have been investigated in depth, little is known about the chemistry of water on stepped surfaces, commonly occurring in realistic situations. Using first-principles simulations, we study the adsorption of water on a stepped platinum surface. We find that water adsorbs preferentially at the step edge, forming linear clusters or chains, stabilized by the cooperative effect of chemical bonds with the substrate and hydrogen bonds. In contrast with their behavior on flat Pt, at steps water molecules dissociate, forming mixed hydroxyl/water structures, through an autocatalytic mechanism promoted by H-bonding. Nuclear quantum effects contribute to stabilize partially dissociated cluster and chains. Together with the recently demonstrated behavior of water chains adsorbed on stepped Pt surfaces to transfer protons via thermally activated hopping, these findings make these systems viable candidates for proton wires.

11.
Faraday Discuss ; 152: 153-67; discussion 203-25, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-22455043

RESUMO

The thermodynamical stability of free, pristine gold clusters at finite temperature, and of cluster+ligands complexes at finite temperature and in the presence of an atmosphere composed of O2 and CO, is studied employing parallel tempering and ab initio atomistic thermodynamics. We focus on Au13, which displays a significant fluxional behavior: Even at low temperature (100 K) this cluster exhibits a multitude of structures that dynamically transform into each other. At finite temperature, the preference of this cluster for three-dimensional versus planar structures is found to result from entropic effects. For gold clusters containing one to four gold atoms in an O2 + CO atmosphere, we apply ab initio atomistic thermodynamics. On the basis of these considerations, we single out a likely reaction path for CO oxidation catalyzed by gold clusters.

12.
Nat Mater ; 8(9): 726-30, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19668207

RESUMO

Surfaces have long been known to have an intricate role in solid-liquid phase transformations. Whereas melting is often observed to originate at surfaces, freezing usually starts in the bulk, and only a few systems have been reported to exhibit signatures of surface-induced crystallization. These include assembly of chain-like molecules, some liquid metals and alloys and silicate glasses. Here, we report direct computational evidence of surface-induced nucleation in supercooled liquid silicon and germanium, and we illustrate the crucial role of free surfaces in the freezing process of tetrahedral liquids exhibiting a negative slope of their melting lines (dT/dP|coexist<0). Our molecular dynamics simulations show that the presence of free surfaces may enhance the nucleation rates by several orders of magnitude with respect to those found in the bulk. Our findings provide insight, at the atomistic level, into the nucleation mechanism of widely used semiconductors, and support the hypothesis of surface-induced crystallization in other tetrahedrally coordinated systems, in particular water in the atmosphere.

13.
J Am Chem Soc ; 130(40): 13460-4, 2008 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-18788811

RESUMO

Inorganic-(bio)organic interfaces are of central importance in many fields of current research. Theoretical and computational tools face the difficult problem of the different time and length scales that are involved and linked in a nontrivial way. In this work, a recently proposed hierarchical quantum-classical scale-bridging approach is further developed to study large flexible molecules. The approach is then applied to study the adsorption of oligopeptides on a hydrophilic Pt(111) surface under complete wetting conditions. We examine histidine sequences, which are well known for their binding affinity to metal surfaces. Based on a comparison with phenylalanine, which binds as strong as histidine under high vacuum conditions but, as we show, has no surface affinity under wet conditions, we illustrate the mediating effects of near-surface water molecules. These contribute significantly to the mechanism and strength of peptide binding. In addition to providing physical-chemical insights in the mechanism of surface binding, our computational approach provides future opportunities for surface-specific sequence design.


Assuntos
Elétrons , Peptídeos/química , Platina/química , Água/química , Adsorção , Simulação por Computador , Modelos Moleculares , Conformação Proteica , Propriedades de Superfície
14.
J Am Chem Soc ; 130(8): 2634-8, 2008 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-18251476

RESUMO

We present a first principle density functional study of phenylalanine interacting with three different classes of surfaces, namely a purely repulsive hard wall, mildly interacting close packed surfaces of group 11 metals (Cu(111), Ag(111), and Au(111)), and strongly interacting close packed surfaces of group 10 metals (Ni(111), Pd(111), and Pt(111)). In particular, we characterize, by changing the substrate, the passage from the statistical behavior of a flexible molecule in the presence of the topological confinement of a hard wall to a purely chemical behavior where the molecule, highly deformed compared to the free state, strongly binds to the surface and statistical conformations play no longer a role. Such a comparative study allows for characterization of some of the key aspects of the adsorption process for a prototype of flexible amino acids on experimentally and technologically relevant metal surfaces.


Assuntos
Grafite/química , Metais/química , Fenilalanina/química , Adsorção , Modelos Químicos , Conformação Molecular , Propriedades de Superfície
15.
J Phys Condens Matter ; 19(17): 176004, 2007 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-21690941

RESUMO

Using first-principles density-functional calculations, we studied the adsorption of methylthiolate (CH(3)S) on (111)-surfaces of the transition metals belonging to group 10 (Ni, Pd, and Pt), and two group 11 metals, Ag and Au. By making a systematic comparison between the different metals, we identify general adsorption properties and clarify them in terms of the interplay between energies, structures and electronic details. On the basis of electron density arguments, we suggest an explanation for the preference of the face-centred cubic (fcc) above the hexagonal close-packed (hcp) hollow site for the adsorption onto (111) metal surfaces. In nanotechnological applications, our analysis may serve to rationalize the optimal choice of the substrate when a given property is required.

16.
J Phys Condens Matter ; 19(24): 242101, 2007 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-21694030

RESUMO

The structure of a water adlayer on a Pt(111) surface is investigated by means of extensive first-principles calculations. Allowing for proton disorder, the ground state energy for the [Formula: see text] structure can be found. This results from an interplay between water/metal chemical bonding and the hydrogen bonding of the water network. This picture is supported by substituting Pt(111) with Ag(111): the almost inert surface allows for the reconstruction of the hydrogen network.

17.
J Phys Condens Matter ; 19(41): 416104, 2007 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-28192336

RESUMO

We report a Car-Parrinello molecular dynamics study of the temperature dependence of the fluid-liquid phase transition in phosphorous, involving the transformation of a molecular fluid phase into a network-like phase. We employed density-functional theory (DFT) with a gradient-corrected functional (B-LYP) to describe the electronic structure and interatomic interactions and performed simulations in a constant pressure ensemble. We spanned a temperature interval ranging from 2500 to 3500 K. With increasing temperature, we found that the structural conversion from the molecular P4 fluid into the network liquid occurs at decreasing pressures, consistent with experimental observations. At lower temperatures the transition is characterized by a sudden increase of density in the sample. The magnitude of the density change decreases with increasing temperature and vanishes at 3500 K. In the temperature range 3100-3500 K we found signals of near- and super-criticality. We identified local structural changes that serve as seeds triggering the overall structural transition.

18.
J Chem Phys ; 122(18): 184510, 2005 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-15918732

RESUMO

We report a Car-Parrinello molecular dynamics study of the liquid-liquid phase transition in phosphorus. We employed a gradient corrected density functional (B-LYP) to describe the electronic structure and performed simulations at constant pressure. Upon increasing pressure we observed, along the 1500 K isotherm, a structural transition converting the molecular P4 liquid into an atomic liquid with a network structure. Our calculations suggest this transition to be first order with a discontinuous density increase accompanied by an insulator into metal transition. The transition pressure is significantly higher than obtained by employing the less accurate local density functional (LDA) [Morishita, Phys. Rev. Lett. 87, 105701 (2001)], which matches the experimental value for the pressure. We argue why the LDA result should be considered fortuitous. The change of the calculated structure factor upon the transition shows the same trend as experimentally observed. Analysis of the structural changes during the phase transition revealed that a chain of linked and opened up ("butterfly") P4 molecules may serve as a seed triggering the transition from the molecular to the network phase.

19.
Phys Rev Lett ; 94(14): 145701, 2005 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-15904077

RESUMO

We determined the phase diagram involving diamond, graphite, and liquid carbon using a recently developed semiempirical potential. Using accurate free-energy calculations, we computed the solid-solid and solid-liquid phase boundaries for pressures and temperatures up to 400 GPa and 12 000 K, respectively. The graphite-diamond transition line that we computed is in good agreement with experimental data, confirming the accuracy of the employed empirical potential. On the basis of the computed slope of the graphite melting line, we rule out the hotly debated liquid-liquid phase transition of carbon. Our simulations allow us to give accurate estimates of the location of the diamond melting curve and of the graphite-diamond-liquid triple point.

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