Ricardo Grau-Crespo

Ricardo Grau-Crespo
University of Reading · Department of Chemistry

PhD

About

170
Publications
70,834
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3,912
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Introduction
Materials theorist at the University of Reading, UK. Working in the application of computer simulation techniques, based on density functional theory and statistical mechanics, to the investigation of materials and minerals.
Additional affiliations
September 2013 - April 2020
University of Reading
Position
  • Professor (Associate)
August 2009 - August 2013
University College London
Position
  • Lecturer
Education
April 2003 - April 2006
Birkbeck, University of London
Field of study
  • Computational Materials Science

Publications

Publications (170)
Article
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Tuning the electronic structure of metal–organic frameworks is the key to extending their functionality to the photocatalytic conversion of absorbed gases. Herein we discuss how the band edge positions in zeolitic imidazolate frameworks (ZIFs) can be tuned by mixing different imidazole-based linkers within the same structure. We present the band al...
Article
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The carbon-carbon coupling via electrochemical reduction of carbon dioxide represents the biggest challenge for using this route as platform for chemicals synthesis. Here we show that nanostructured iron (III) oxyhydroxide on nitrogen-doped carbon enables high Faraday efficiency (97.4%) and selectivity to acetic acid (61%) at very-low potential (-0...
Article
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Sequence-selective intercalation of pyrene into the chain-folds of a random, binary copolyimide under fast-exchange conditions results in the development of self-similar structure in the diimide region of the 1H NMR spectrum. The resulting spectrum can be described by the mathematics of fractals, an approach that is rationalised in terms of a dynam...
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Recently, high solar-to-hydrogen efficiencies were demonstrated using La and Rh co-doped SrTiO3 (La,Rh:SrTiO3) incorporated into a low-cost and scalable Z-scheme device, known as a photocatalyst sheet. However, the unique properties that enable La,Rh:SrTiO3 to support this impressive performance are not fully understood. Combining in situ spectroel...
Article
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The sensitivity of NMR to the local environment, without the need for any long-range order, makes it an ideal tool for the characterisation of disordered materials. Computational prediction of NMR parameters can be of considerable help in the interpretation and assignment of NMR spectra of solids, but the statistical representation of all possible...
Article
Using a combination of experiments and calculations, we have gained new insights into the nature of anion–cation interactions in ionic liquids (ILs). An X-ray photoelectron spectroscopy (XPS)-derived anion-dependent electrostatic interaction strength scale, determined using XPS core-level binding energies for IL cations, is presented here for 39 di...
Article
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When considering the possibility of storing information in the sequence of monomer residues within an AB-type copolymer chain, it is constructive to model that sequence as a string of ones and zeros. The intramolecular environment around any given digit (say a “1”) can then be represented by another string of integers—a code—obtained by summing pai...
Article
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The significance of interfacial thermal resistance in the thermal conductivity of nanofluids is not well understood, in part because of the absence of measurements of this quantity. Here, we study the interfacial thermal resistance for metal–oil nanofluids of interest as heat transfer fluids for concentrating solar power, using density functional t...
Article
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Defect pyrochlores are promising candidates for thermally-insulating materials for use in technological applications. Preparation of materials of general formula K 1-x Cs x Ta 1-y Nb y WO 6 (0 ≤ x ≤ 1; y = 0, 0.5) has...
Article
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Spinel ferrites exhibit significant promise in photocatalysis and other applications due to their compositional diversity and favourable electronic structure, magnetism, and partially tuneable cation distribution (inversion degree). However, their complex...
Article
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Ternary pnictide semiconductors with II–IV–V2 stoichiometry hold potential as cost-effective thermoelectric materials with suitable electronic transport properties, but their lattice thermal conductivities (κ) are typically too high. Insights into their vibrational properties are therefore crucial to finding strategies to reduce κ and achieve impro...
Preprint
Full-text available
Ternary pnictides semiconductors with II-IV-V2 stoichiometry hold potential as cost effective thermoelectric materials with suitable electronic transport properties, but their lattice thermal conductivities ($\kappa$) are typically too high. Gaining insight into their vibrational properties is therefore crucial to finding strategies to reduce $\kap...
Article
Hydrogen bonds (HBs) play an important role in the rotational dynamics of organic cations in hybrid organic/inorganic halide perovskites, thus affecting the structural and electronic properties of the perovskites. However, the properties and even the existence of HBs in these perovskites are not well established. In this study, we investigate HBs i...
Preprint
Full-text available
The generation of plausible crystal structures is often an important step in the computational prediction of crystal structures from composition. Here, we introduce a methodology for crystal structure generation involving autoregressive large language modeling of the Crystallographic Information File (CIF) format. Our model, CrystaLLM, is trained o...
Article
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Thermoelectric materials can be used to construct devices which recycle waste heat into electricity. However, the best known thermoelectrics are based on rare, expensive or even toxic elements, which limits their widespread adoption. To enable deployment on global scales, new classes of effective thermoelectrics are thus required. Ab initio models...
Preprint
Hydrogen bonds (HBs) play an important role in the rotational dynamics of organic cations in hybrid organic/inorganic halide perovskites, affecting the structural and electronic properties of the perovskites. However, the properties and even the existence of HBs in these perovskites are not well established. We investigate HBs in perovskites MAPbBr...
Article
Full-text available
Using grand canonical thermodynamic analysis with inputs from DFT calculations we calculated equilibrium molar fractions of copper vacancies (VCu), H interstitials (Hi) and their complexes in bulk Cu in a wide range of temperature and hydrogen pressure values. The results show that the equilibrium molar fractions of both VCu and Hi are low in most...
Presentation
Full-text available
Stress-induced voiding (SIV) is amongst the most commonly reported defects in metallic systems [1]. Supersaturation of vacancies is considered an initial stage of voiding in metals [2]. It is generally known that H promotes the formation of vacancies, thus, it is anticipated that H will play a significant role in voiding phenomena [3, 4]. However,...
Article
ABX 3 molecular perovskites have recently gained attention in the field of ferroelectrics and barocalorics where the materials’ mechanical properties such as mechanical stability, compressibility, hardness, and elasticity are important performance...
Article
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Nanostructuring is a well-established approach to improve the thermoelectric behavior of materials. However, its effectiveness is restricted if excessively small particle sizes are necessary to considerably decrease the lattice thermal...
Preprint
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ABX3 molecular perovskites have recently gained attention in the field of ferroelectrics and barocalorics where the materials’ mechanical properties such as mechanical stability, compressibility, hardness, and elasticity are important performance criteria. Akin to previous work on ceramic perovskites, research on molecular perovskites benefits from...
Preprint
Thermoelectric materials can be used to construct devices which recycle waste heat into electricity. However, the best known thermoelectrics are based on rare, expensive or even toxic elements, which limits their widespread adoption. To enable deployment on global scales, new classes of effective thermoelectrics are thus required. $\textit{Ab initi...
Article
Full-text available
We demonstrate a combined experimental and computational approach to probe the electronic structure and atomic environment of an ionic liquid, based on core level binding energies. The 1-butyl-3-methylimidazolium thiocyanate [C4C1Im][SCN] ionic liquid was studied using ab initio molecular dynamics, and results were compared against previously publi...
Article
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Chalcopyrite, CuFeS2 is considered one of the promising n-type thermoelectric materials with high natural abundance as a mineral. In this work, partial substitution of germanium in materials CuFe1−xGexS2, (0.0 ≤ x ≤ 0.10), leads to an almost six-fold enhancement of thermoelectric properties. X-Ray photoelectron spectroscopy (XPS) reveals that germa...
Article
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Bismuth ferrite, BiFeO3, is a multiferroic solid that is attracting increasing attention as a potential photocatalytic material, because the ferroelectric polarization enhances the separation of photogenerated carriers. With the motivation of finding routes to engineer the band gap and the band alignment, while conserving or enhancing the ferroelec...
Article
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Ab initio prediction of the variation of properties in the configurational space of solid solutions is computationally very demanding. We present an approach to accelerate these predictions via a combination of density functional theory and machine learning, using the cubic spinel nitride GeSn2N4 as a case study, exploring how formation energy and...
Article
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The chemistry of interfaces and its relation with energy storage at and transport through solid-liquid interfaces in heat transfer nanofluids is a very unexplored terrain. Here we discuss how the magnitude of the changes in specific heat and thermal conductivity of the base fluid, upon dispersion of a nanomaterial, depends on the surface chemistry...
Article
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The dearth of n-type sulfides with thermoelectric performance comparable to that of their p-type analogues presents a problem in the fabrication of all-sulfide devices. Chalcopyrite (CuFeS2) offers a rare example of an n-type sulfide. Chemical substitution has been used to enhance the thermoelectric performance of chalcopyrite through preparation o...
Preprint
Ab initio prediction of the variation of properties in the configurational space of solid solutions is computationally very demanding. We present an approach to accelerate these predictions via a combination of density functional theory and machine learning, using the cubic spinel nitride GeSn$_2$N$_4$ as a case study, exploring how formation energ...
Article
The presence of bromine as a trace-element in calcium carbonate speleothems constitutes a useful proxy of past volcanic activity, thus helping to provide input parameters for climate model simulations and risk assessment. However, the chemical nature of bromine-containing impurities in the calcium carbonate phases forming speleothems is not underst...
Article
Full-text available
The use of machine learning is becoming increasingly common in computational materials science. To build effective models of the chemistry of materials, useful machine-based representations of atoms and their compounds are required. We derive distributed representations of compounds from their chemical formulas only, via pooling operations of distr...
Preprint
Full-text available
BiFeO3 is a multiferroic solid that is of interest as a potential photovoltaic and photocatalytic material. The ferroelectric character might enhance carrier separation, but the efficiency is limited by a wide electronic bandgap. With the motivation of finding routes to engineer the bandgap and the band structure, we have investigated the thermodyn...
Article
Mixed-anion mixed-cation perovskites with (FAPbI 3 ) 1-x (MAPbBr 3 ) x composition have allowed record efficiencies in photovoltaic solar cells, but their atomic-scale behaviour is not well understood yet, in part because their theoretical modelling requires...
Article
Full-text available
Demonstrating both the intrinsic and extrinsic nature of the giant piezoelectric effect (GPE) in complex solid solutions, near the morphotropic phase boundary, has been extremely challenging until now, because such materials exhibit multiple phases on the order of tens of microns across, meaning important information is lost due to averaging when u...
Preprint
Full-text available
Mixed-anion mixed-cation perovskites with (FAPbI$_3$)$_{1-x}$(MAPbBr$_3$)$_x$ composition have allowed record efficiencies in photovoltaic solar cells, but their atomic-scale behaviour is not well understood yet, in part because their theoretical modelling requires consideration of complex and interrelated dynamic and disordering effects. We presen...
Preprint
Full-text available
The use of computer simulation to predict the lattice thermal conductivity of materials has the potential to accelerate the discovery of new thermoelectric materials. However, the accurate prediction of this property from first principles, without input from experiment, is very computationally demanding, which limits the use of high-throughput stra...
Preprint
The use of computer simulation to predict the lattice thermal conductivity of materials has the potential to accelerate the discovery of new thermoelectric materials. However, the accurate prediction of this property from first principles, without input from experiment, is very computationally demanding, which limits the use of high-throughput stra...
Article
Full-text available
Molecular perovskites, i.e. ABX3 coordination polymers with a perovskite structure, are a chemically diverse material platform for studying fundamental and applied materials properties such as barocalorics and improper ferroelectrics. Compared to inorganic perovskites, the use of molecular ions on the A- and X-site of molecular perovskites leads to...
Preprint
Full-text available
The use of machine learning is becoming increasingly common in computational materials science. To build effective models of the chemistry of materials, useful machine-based representations of atoms and their compounds are required. We derive distributed representations of compounds from their chemical formulas only, via pooling operations of distr...
Article
Full-text available
Sulfur and molybdenum trace impurities in speleothems (stalagmites and stalactites) can provide long and continuous records of volcanic activity, which are important for past climatic and environmental reconstructions. However, the chemistry governing the incorporation of the trace element-bearing species into the calcium carbonate phases forming s...
Preprint
Full-text available
The presence of bromine as a trace-element in calcium carbonate speleothems constitutes a useful proxy of past volcanic activity, thus helping to provide input parameters for climate model simulations and risk assessment. However, the chemical nature of bromine-containing impurities in the calcium carbonate phases forming speleothems is not underst...
Preprint
Full-text available
The presence of bromine as a trace-element in calcium carbonate speleothems constitutes a useful proxy of past volcanic activity, thus helping to provide input parameters for climate model simulations and risk assessment. However, the chemical nature of bromine-containing impurities in the calcium carbonate phases forming speleothems is not underst...
Article
Full-text available
Computer simulations of alloys’ properties often require calculations in a large space of configurations in a supercell of the crystal structure. A common approach is to map density functional theory results into a simplified interaction model using so-called cluster expansions, which are linear on the cluster correlation functions. Alternative des...
Preprint
Full-text available
p>Sulphur and molybdenum trace impurities in speleothems (stalagmites and stalactites) can provide long and continuous records of volcanic activity, which are important for past climatic and environmental reconstructions. However, the chemistry governing the incorporation of the trace-element bearing species into the calcium carbonate phases formin...
Article
Full-text available
Understanding how adsorbates influence polaron behavior is of fundamental importance in describing the catalytic properties of TiO2. Carboxylic acids adsorb readily at TiO2 surfaces, yet their influence on polaronic states is unknown. Using UV photoemission spectroscopy (UPS), two-photon photoemission spectroscopy (2PPE), and density functional the...
Article
Full-text available
Metal-organic frameworks (MOFs) are promising photocatalytic materials due to their high surface area and tuneability of their electronic structure. We discuss here how to engineer the band structures and optical properties of a family of two-dimensional porphyrin-based MOFs, consisting of M-tetrakis(4-carboxyphenyl)porphyrin structures (M-TCPP, wh...
Article
Concentrating solar power (CSP) technology can become a very valuable contributor to the transformation and decarbonization of our energy landscape, but for this technology to overcome the barrier toward market deployment, significant enhancements in the solar-to-thermal-to-electric energy conversion efficiency are needed. Here, an in-depth experim...
Article
It is well known that the specific heat of a heat transfer fluid can be significantly improved by the addition of nanoparticles to form a so-called nanofluid, but the origin of the effect is not completely understood yet. Here, we use molecular dynamics simulations in a nanofluid consisting of palladium nanoparticles in a commercial heat transfer f...
Preprint
Full-text available
Metal organic frameworks (MOFs) are promising photocatalytic materials due to their high surface area and tuneability of their electronic structure. We discuss here how to engineer the band structures and optical properties of a family of two-dimensional (2D) porphyrin-based MOFs, consisting of M tetrakis(4 carboxyphenyl)porphyrin structures (M TCP...
Article
Full-text available
Co-polycondensation of the diimide-based diols N,N'-bis(2-hydroxyethyl)hexafluoroisopropylidene-diphthalimide, (HFDI), and N,N'-bis(2-hydroxy-ethyl)naphthalene-1,4,5,8-tetracarboxylic-diimide, (NDI), with aliphatic diacyl chlorides ClOC(CH2) x COCl (x = 5 to 8) affords linear copoly(ester-imide)s. Such copolymers interact with pyrene via supramole...
Article
Nanofluids have emerged as an addition for thermal management and energy conversion applications. The dispersion of a small amount of solid nanoparticles occasionally leads to an unexpected enhancement in the specific heat of the dispersant fluid. This effect has technical, economic and social significance, and for that it has received a lot of att...
Article
Full-text available
Understanding the interaction of amino acids with metal surfaces is essential for the rational design of chiral modifiers able to confer enantioselectivity to metal catalysts. We present here an investigation of the adsorption of aspartic acid (Asp) on the Ni{100} surface, using a combination of synchrotron X-Ray Photoelectron Spectroscopy (XPS) an...
Article
Marked increases in sulfur and molybdenum concentration in stalagmites have been proposed as possible evidence of volcanic activity in the past. Thus, speleothems have great potential to deliver long and continuous records of volcanic activity. However, little is known about the chemical nature of these impurities in the calcium carbonate (CaCO3) p...
Article
Full-text available
The properties of graphite, and of few-layer graphene, can be strongly influenced by the edge structure of the graphene planes, but there is still much that we do not understand about the geometry and stability of these edges. We present an experimental and theoretical study of the closed edges of graphite crystals, and of the effect of an electric...
Preprint
Co-polycondensation of the diimide-based diols N , N '-bis(2-hydroxyethyl)hexafluoro-isopropylidene-diphthalimide, (HFDI), and N , N '-bis(2-hydroxy-ethyl)naphthalene-1,4,5,8-tetracarboxylic-diimide, (NDI), with aliphatic diacyl chlorides ClOC(CH<sub>2</sub>) <sub>x</sub> COCl ( x = 5 to 8) affords linear copoly(ester-imide)s. Such copolymers inter...
Article
Nano-colloidal suspensions of nanomaterials in a fluid, nanofluids, are appealing because of their interesting properties related to heat transfer processes. Whilst nanomaterials based on transition metal chalcogenides (TMCs) have been widely studied in catalysis, sensing, and energy storage applications, there are few studies of nanofluids based o...
Article
Full-text available
Polycondensation of the diimide-based diols N,N'-bis(2-hydroxyethyl)hexafluoro-isopropylidene-diphthalimide (HFDI), N,N'-bis(2-hydroxyethyl)pyromellitimide (PMDI), or N,N'-bis(2-hydroxyethyl)naphthalene-1,4,5,8-tetracarboxylic-diimide (NDI) with aliphatic diacyl chlorides ClOC(CH2)xCOCl (x = 1 to 8) affords linear poly(ester-imide)s. Homopolymers b...
Article
Semiconducting quaternary chalcogenides with A2ZnBQ4 stoichiometry, where A and B are monovalent and tetravalent metal ions and Q is a chalcogen element (e.g. Cu2ZnSnS4 or CZTS) have recently attracted considerable attention as potential solar-cell absorbers made from abundant and non-toxic elements. Unfortunately, they exhibit relatively poor sunl...