Ab Initio Screening Research Articles

Phase stability and mechanical property trends for MAB phases by high-throughput ab initio calculations

MAB phases (MABs) are atomically-thin laminates of ceramic/metallic-like layers, having made a breakthrough in the development of 2D materials. Though offering a vast chemical and phase space, relatively few MABs have been synthesised. To guide experiments, we perform high-throughput ab initio screening of MABs that combine group 4–7 transition metals (M); Al, Si, Ga, Ge, or In (A); and boron (B) focusing on their phase stability trends and mechanical properties. Considering the 1:1:1, 2:1:1, 2:1:2, 3:1:2, 3:1:3, and 3:1:4 M:A:B ratios and 10 phase prototypes, synthesisability of a single-phase compound for each elemental combination is estimated through formation energy spectra of competing dynamically stable MABs. Based on the volumetric proximity of energetically-close phases, we identify systems in which volume-changing deformations may facilitate transformation toughening. Subsequently, chemistry- and phase-structure-related trends in the elastic stiffness and ductility are predicted using elastic-constants-based descriptors. The analysis of directional Cauchy pressures and Young's moduli allows comparing mechanical response parallel and normal to M–B/A layers. The suggested promising MABs include Nb3AlB4, Cr2SiB2, Mn2SiB2 or the already synthesised MoAlB.

Unveiling the gas sensing potential of CxNy monolayer through ab initio screening

The development of superior performance and safety metal free sensors for harmful gas detection is of great significance, but it is still challenging. In this study, we developed a new strategy denoted as ‘5S’ (stability, sensitivity, selectivity, speed recovery time and safety) to screen CxNy (x:2∼5, y:1∼8) monolayer as outstanding performance gas sensors (NO, NO2, NH3, CO and CO2) via density functional theory (DFT). The results indicate that all gas molecules are adsorbed on the CxNy surface due to the negative adsorption energy; interestingly, the electron transfer changes slightly during the interaction between CxNy and the adsorbed gas molecules. The adsorption energy of C2N, C3N4, C3N5, C5N8 for NO2 hazardous gas is particularly pronounced and difficult to desorb from CxNy compared to the other candidate CxNy, which suggests that it hinders to be a promising gas sensor. Conversely, the adsorption energies of C2N and C5N8 for small gas molecules are too small, resulting in insufficient sensibility. It is worth noting that C3N4, C3N5 is a potential candidate substrate for NO due to its optimized adsorption/desorption properties and fast recovery time. Furthermore, C3N4 can be used as a gas sensor for NH3 due to its suitable adsorption/desorption properties and fast recovery time compared to other substrates. This work not only theoretically screens C3N5 and C3N4 substrates for excellent performance as gas sensors, but also provides a new ‘5S’ screening strategy for other 2D materials as candidates for gas sensors.

Ab initio screening of two-dimensional CuQ x and AgQ x chalcogenides

Two-dimensional (2D) chalcogenides have attracted great interest from the scientific community due to their intrinsic physical–chemical properties, which are suitable for several technological applications. However, most of the reported studies focused on particular compounds and composition, e.g., MoS2, MoSe2, WS2, and WSe2. Thus, there is an increased interest to extend our knowledge on 2D chalcogenides. Here, we report a density functional theory (DFT) screening of 2D coinage-metal chalcogenides (MQ x ), where M = Cu, Ag, Q = S, Se, Te, x = 0.5, 1.0, 1.5, 2.0, with the aim to improve our atomistic understanding of the physical–chemical properties as a function of cation (M), anion (Q), and composition (x). Based on 258 DFT calculations, we selected a set of 22 stable MQ x monolayers based on phonons analyses, where we identified 9 semiconductors (7 AgQ x and 2 CuQ x ), with band gaps from 0.07 eV up to 1.67 eV, while the remaining systems have a metallic character. Using all 258 systems, we found a logarithmic correlation between the average weighted bond lengths and effective coordination number of cations and anions. As expected, the monolayer cohesive energies increase with the radius of the Q species (i.e., from S to Te). Furthermore, an increase in the anion size diminishes the work function for nearly all MQ x monolayers, which can be explained by the nature of the electronic states at the valence band maximum.

A new protonated molecule discovered in TMC-1: HCCNCH+

In recent years we have seen an important increase in the number of protonated molecules detected in cold dense clouds. Here we report the detection in TMC-1 of HCCNCH+, the protonated form of HCCNC, which is a metastable isomer of HC3N. This is the first protonated form of a metastable isomer detected in a cold dense cloud. The detection was based on observations carried out with the Yebes 40 m telescope and the 30 m telescope of the Institut de Radioastronomie Millimétrique (IRAM), which revealed four harmonically related lines. We derived a rotational constant B = 4664.431891 ± 0.000692 MHz and a centrifugal distortion constant D = 519.14 ± 4.14 Hz. From a high level ab initio screening of potential carriers, we confidently assigned the series of lines to the ion HCCNCH+. We derived a column density of (3.0 ± 0.5) × 1010 cm−2 for HCCNCH+, which results in a HCCNCH+/HCCNC abundance ratio of 0.010 ± 0.002. This value is well reproduced by a state-of-the-art chemical model which, however, is subject to important uncertainties regarding the chemistry of HCCNCH+. The observational and theoretical status of protonated molecules in cold dense clouds indicate that there exists a global trend in which protonated-to-neutral abundance ratios MH+/M increase with increasing proton affinity of the neutral M, although if one is restricted to species M with high proton affinities (> 700 kJ mol−1), MH+/M ratios fall in the range 10−3–10−1, with no apparent correlation with the proton affinity. We suggest various protonated molecules that are good candidates for detection in cold dense clouds in the near future.

Ab initio screening of refractory nitrides and carbides for high temperature hydrogen permeation barriers

Density functional theory was used to screen eleven refractory materials – two pure metals, six nitrides, and three carbides–as high-temperature hydrogen permeation barriers to prevent hydrogen embrittlement. Activation energies were calculated for atomic hydrogen (H) diffusion into the first subsurface layer from the lowest energy surface of the high-temperature phase of each candidate material. The candidate barrier materials with the highest activation energies are h-BN, c-BN, HfN, and ZrN with predicted barriers of 3.25 eV, 3.23 eV, 3.14 eV, and 2.76 eV, respectively. Strain energies, Bader charges, and density of states were calculated for the diffusing H at the relaxed initial state and the transition state to provide insight into contributing factors to high energy barriers. The diffusing H atom in materials with the highest predicted barriers are protic. In addition, interstitial H atoms induce mid-gap states in the density of states of both BN polymorphs. The nitrogen retention of each nitride material at high temperatures was predicted using nitrogen vacancy formation energies with respect to gaseous nitrogen. Experimental evaluation of nitrogen retention in h-BN, ZrN, and TiN confirmed their resistance to nitrogen loss at 1773 K. However, of these nitrides, TiN is predicted to be the least stable. This work identifies multiple promising materials that are predicted to be effective hydrogen barriers at high temperatures and that are stable at temperatures above 2700 K, with BN predicted to perform best.

A density functional study of electronic and optical properties of perovskite (CH3CH2NH3PbI3) for photovoltaic cell application

In this study, we have performed ab-initio screening of the ethylammonium cation-based hybrid perovskite ethylammonium lead iodide (CH3CH2NH3PbI3or EPI) as the prospective absorber material for fabricating cost-effective and energy-efficient photovoltaic devices. The extensively studied methylammonium lead iodide (CH3NH3PbI3 or MPI) exhibits high efficiency but has serious environmental and stability related concerns due to leakage of lead. Therefore, we intend to replace (CH3NH3+or M+) cation in MPI with (CH3CH2NH3+or E+) and expect that so formed perovskite EPI would prove to be an eco-friendlier and more stable photovoltaic absorber material. In this investigation, we have employed FP-LAPW+lo method under density functional theory as provided in WIEN2k simulation code. We have employed a more accurate Tb-mBJ exchange correlation potential to calculate physical properties like energy bandgap, density of states, optical parameters and SLME relevant to photovoltaic applications. According to the findings of this study, EPI is direct bandgap material with bandgap of 2.17 eV at k-point R with optical absorption coefficient higher than 104 cm−1, which endorses it as a suitable photovoltaic absorber material. The dependence of optical coefficients on angular frequency of incident electromagnetic radiation has also been discussed. The theoretical power conversion efficiency comes out to be 18.9%.

Interstellar detection of the simplest aminocarbyne H2NC: an ignored but abundant molecule

We report the first identification in space of H2NC, a high-energy isomer of H2CN that has been largely ignored in chemical and astrochemical studies. The observation of various unidentified lines around 72.2 GHz in the cold dark cloud L483 motivated the search and successful detection of additional groups of lines in harmonic relation. Following an exhaustive high-level ab initio screening of possible carriers, we confidently assign the unidentified lines to H2NC based on the good agreement between the astronomical and theoretical spectroscopic parameters alongside sound spectroscopic and astrochemical arguments. The observed frequencies are used to precisely characterize the rotational spectrum of H2NC. This species is also detected in the cold dark cloud B1-b and the z = 0.89 galaxy in front of the quasar PKS 1830−211. We derive H2NC/H2CN abundance ratios ~1 in L483 and B1-b and 0.27 toward PKS 1830−211. Neither H2NC nor H2CN are detected in the dark cloud TMC-1, which seriously undermines the previous identification of H2CN in this source. We suggest that the H2NC/H2CN ratio behaves as the HNC/HCN ratio, with values close to one in cold dense clouds and below one in diffuse clouds. The reactions N + CH3 and C + NH3 emerge as strong candidates for the production of H2NC in interstellar clouds. Further studies on these two reactions are needed to evaluate the yield of H2NC. Due to the small number of atoms involved, it should be feasible to constrain the chemistry behind H2NC and H2CN, just as has been done for HNC and HCN, as this could allow for the H2NC/H2CN ratio to be applied as a probe of chemical or physical conditions of the host clouds.

Ab initio screening of zeolite Y formulations for efficient adsorption of thiophene in presence of benzene

In the context of deep desulfurization of transport fuels, the present work aimed at identifying a suitable material for the selective removal of thiophene from fuels. Dispersion corrected density functional theory (DFT) calculations have been carried out in order to investigate the adsorption of benzene and thiophene in various faujasite zeolite formulations including DAY, HY, LiY, NaY, KY, CsY, Cu(I)Y, Cu(II)Y, Ag(I)Y, Zn(II)Y, and FAU containing Lewis acid sites (LAS) (defect or extra-framework). Bearing-LAS FAU, Cu(I)Y, Cu(II)Y, Zn(II)Y, CsY, and HY showed a higher affinity towards thiophene adsorption. In particular, thiophene is more adsorbed on defect LAS than benzene by 17.7 kJ/mol, suggesting that this zeolite could be chosen as a suitable candidate for the optimal selective adsorption of thiophene in the presence of benzene. In terms of regenerability, all formulations can be safely used (except the one containing extra-framework Lewis acid sites) as they can limit the activation of the C-S bond of thiophene. Considering both adsorption selectivity and sorbent regenerability criteria, faujasites containing defect Lewis acid sites could be chosen as a good compromise to perform a selective adsorption of thiophene in presence of benzene.

High-temperature conventional superconductivity in the boron-carbon system: Material trends

In this work we probe the possibility of high-temperature conventional superconductivity in the boron-carbon system, using ab-initio screening. A database of 320 metastable structures with fixed composition (50$\%$/50$\%$) is generated with the Minima-Hopping method, and characterized with electronic and vibrational descriptors. Full electron-phonon calculations on sixteen representative structures allow to identify general trends in $T_{\textrm{c}}$ across and within the four families in the energy landscape, and to construct an approximate $T_{\textrm{c}}$ predictor, based on transparently interpretable and easily computable electronic and vibrational descriptors. Based on these, we estimate that around 10$\%$ of all metallic structures should exhibit $T_{\textrm{c}}$'s above 30 $K$. This work is a first step towards ab-initio design of new high-$T_{\textrm{c}}$ superconductors.

First-Principles Study of Structural Transitions in LiNiO2 and High-Throughput Screening for Long Life Battery

Herein, we performed ab initio screening to identify the best doping of LiNiO2 to achieve improved cycle performance in lithium ion batteries. The interlayer interaction that dominates the c-axis contraction and overall performance was captured well by density functional theory using van der Waals exchange-correlation functionals. The screening indicated that Nb-doping is promising for improving cycle performance. To extract qualitative reasonings, we performed data analysis in a materials informatics manner to obtain a reasonable regression to reproduce the obtained results. LASSO analysis implied that the charge density between the layers in the discharged state is the dominant factor influencing cycle performance.

Unraveling the Factors Behind the Efficiency of Hydrogen Evolution in Endohedrally Doped C60 Structures via Ab Initio Calculations and Insights from Machine Learning Models

AbstractUnderstanding the origins of catalytic activity (or inactivity) in nanostructures allows for the rational design of cheap and durable catalysts. Here, consistent and comprehensive ab initio screening of endohedrally doped fullerenes as potential catalysts for hydrogen evolution reactions is performed. By examining variations in the electronic structure of the carbon atoms in the presence of the dopant, and by relying on machine learning algorithms, the origin of enhanced activity in fullerenes can be underpinned. The effect is attributed to the formation of free radicals by weakening the C─C double bonds. A number of electronic descriptors are discussed which can be fed into machine learning models to efficiently and reliably predict catalytic activities. This allows for a generalization of trends and a predictive ability that could be applied to other fullerene structures.

Materials genomics‐guided ab initio screening of MOFs with open copper sites for acetylene storage

Discovering high‐performance metal‐organic frameworks (MOFs) with open metal sites has become an increasingly hot research topic in the field of safe storage and transportation of acetylene. Following the concept of Materials Genomics proposed recently, a database of 502 experimental MOFs was built by searching the structures deposited in the CSD with the dicopper paddle‐wheel node Cu2(COO)4 as the characteristic materials gene. On the basis of the developed ab initio force field, a high‐throughput computational screening was conducted to examine the property‐performance relationships of MOFs containing Cu‐OMS for C2H2 storage at ambient conditions. The optimal ranges of the structural and energetic features for the design of such MOFs were suggested. From our computational screening, three potentially promising MOFs were identified which exhibit a performance outperforming those MOFs reported experimentally so far with record high gravimetric C2H2 uptakes, both in the total and deliverable adsorption capacities. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1389–1398, 2018

Quantifying the Performance of P-Type Transparent Conducting Oxides by Experimental Methods.

Screening for potential new materials with experimental and theoretical methods has led to the discovery of many promising candidate materials for p-type transparent conducting oxides. It is difficult to reliably assess a good p-type transparent conducting oxide (TCO) from limited information available at an early experimental stage. In this paper we discuss the influence of sample thickness on simple transmission measurements and how the sample thickness can skew the commonly used figure of merit of TCOs and their estimated band gap. We discuss this using copper-deficient CuCrO as an example, as it was already shown to be a good p-type TCO grown at low temperatures. We outline a modified figure of merit reducing thickness-dependent errors, as well as how modern ab initio screening methods can be used to augment experimental methods to assess new materials for potential applications as p-type TCOs, p-channel transparent thin film transistors, and selective contacts in solar cells.

Model dielectric function for 2D semiconductors including substrate screening

Dielectric screening of excitons in 2D semiconductors is known to be a highly non-local effect, which in reciprocal space translates to a strong dependence on momentum transfer q. We present an analytical model dielectric function, including the full non-linear q-dependency, which may be used as an alternative to more numerically taxing ab initio screening functions. By verifying the good agreement between excitonic optical properties calculated using our model dielectric function, and those derived from ab initio methods, we demonstrate the versatility of this approach. Our test systems include: Monolayer hBN, monolayer MoS2, and the surface exciton of a 2 × 1 reconstructed Si(111) surface. Additionally, using our model, we easily take substrate screening effects into account. Hence, we include also a systematic study of the effects of substrate media on the excitonic optical properties of MoS2 and hBN.

Ultralow Thermal Conductivity in Full Heusler Semiconductors.

Semiconducting half and, to a lesser extent, full Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full Heusler compounds with ten valence electrons (X_{2}YZ, X=Ca, Sr, and Ba; Y=Au and Hg; Z=Sn, Pb, As, Sb, and Bi) through high-throughput abinitio screening. These new compounds exhibit ultralow lattice thermal conductivity κ_{L} close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials.

(Invited) Molecular Understanding of Oxygen Exchange in Solid Oxide Fuel Cell Cathodes

Materials with the ability to rapidly exchange oxygen with the environment play a critical role in many existing and developing technologies, e.g., solid oxide fuel cells (SOFCs), gas separation membranes, oxygen sensors, chemical looping devices, and memristors. In particular, reducing the working temperature of SOFCs, which is critical to their increased commercialization, is significantly inhibited by the slow oxygen exchange kinetics at the cathode. The oxygen exchange is an essential step in the overall oxygen reduction reaction (ORR), where O2 (gas) combines with 4e- to incorporate as 2O2- into the electrolyte, facilitated by the cathode. Oxygen exchange rates are typically quantified by the oxygen exchange coefficient, K*, which represents the response of the rate of oxygen exchange to a driving force. In our work we are developing techniques to predict K* and provide a molecular scale understanding of processes involved in oxygen surface exchange, with the long-term goal of designing more active oxygen exchange materials. Our work has focused on perovskite materials. A few years ago we identified the distance of the bulk oxygen 2p-band center to the Fermi level as an easily calculated descriptor for oxygen exchange in electronic conducing perovskites.[1] These results suggested that overall oxyphilicity plays a critical role in determining K* and provides a tool for high-throughput ab initio screening of promising materials. We will report on recent predictions of active oxygen exchange systems using these screening approaches. In more recent work we have initiated an effort to model oxygen exchange at the molecular level for the (La,Sr)CoO3-d (LSC) system. Using ab inito energetics and the elementary kinetics formalism developed by Adler, et al.[2] We have modeled the possible reaction steps on the LSC (001) surface. This modeling has yielded valuable insights in the rate limiting steps of oxygen exchange through a perovskite surface, the role of surface termination and Sr segregation on K*,[3, 4] and the absolute limits of surface exchange rates. Acknowledgement We gratefully acknowledge financial support from the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award number DE-SC0001284, and computing support from NSF National Center for Supercomputing Applications (NCSA - DMR060007).

High-throughput ab initio screening for two-dimensional electride materials.

High-throughput ab initio screening of approximately 34000 materials in the Materials Project was conducted to identify two-dimensional (2D) electride materials, which are composed of cationic layers and anionic electrons confined in a 2D empty space. The screening was based on three indicators: (1) a positive total formal charge per formula unit; (2) layered structures for two-dimensionality; (3) empty spaces between the layer units. Three nitrides, Ca2N, Sr2N, and Ba2N, and the carbide Y2C were identified as 2D electrides, where Ca2N is the only experimentally confirmed 2D electride (Lee, K.; et al. Nature 2013, 494, 336-341). Electron density analysis using ionic radii revealed a smaller number of anionic electrons in Y2C than those in the three nitrides as a result of the partial occupation of the anionic electrons in the d orbitals of Y. In addition, no candidates were identified from the p-block elements, and thus the ab initio screening indicates that the s-block elements (i.e., alkali or alkaline-earth metals) are highly preferable as cation elements. To go beyond the database screening, a tailored modeling was conducted to determine unexplored compounds including the s-block elements that are suitable for 2D electrides. The tailored modeling found that (1) K2Cl, K2Br, Rb2Cl, and Rb2Br dialkali halides are highly plausible candidates, (2) Li2F and Na2Cl dialkali halides are highly challenging candidates, and (3) the Cs2O(1-x)F(x) halogen-doped dialkali oxide is a promising candidate.

Ab initio screening methodology applied to the search for new permanent magnetic materials

In this paper a computational high-throughput screening (HTS) approach to the search for alternative permanent magnetic materials is presented. Systems considered for a start are binary intermetallic compounds composed of rare-earth (RE) and transition metal (TM) elements. With the tight-binding-linear muffin-tin-orbital-atomic-sphere-approximation (TB-LMTO-ASA) method of density functional theory (DFT) a variety of RE–TM intermetallic phases is investigated and their magnetic properties are obtained at rather low computational costs. Next, interstitial elements such as boron, carbon and nitrogen in these phases are considered. For promising candidate phases with high and stable spontaneous ferromagnetic polarization, the calculated local magnetic moments and exchange coupling parameters, as obtained from TB-LMTO-ASA calculations, are then used for Monte Carlo simulations to identify candidates with sufficiently high Curie temperatures (Tc). Finally, magnetocrystalline anisotropy constants (K1) of the most promising candidate phases are calculated with accurate, potential-shape-unrestricted DFT calculations using the Vienna ab initio simulation package. The computational HTS procedure is illustrated by results for a selection of hard-magnetic RE–TM phases like RETM5, RE2TM17 and RE2TM14B.

High-throughput ab initio screening of binary solid solutions in olivine phosphates for Li-ion battery cathodes

A promising approach to improving the performance of iron-phosphate FePO4 cathode materials for Li-ion batteries is to partly or fully substitute Fe with other metals. Here, we use high-throughput density-functional theory (DFT) calculations to investigate binary mixtures of metal atoms M and M′ in (Li)MyM′1−yPO4 olivine phosphates. We determine the formation energy for various stoichiometries of different binary combinations of metals for the cases of full lithiation and delithiation. Systematic screening of all combinations of Fe and Mn with elements of the 3d transition-metal (TM) series allows us to identify trends with average band filling and atomic size. We also included compounds that verify the observed relations or that were discussed as cathode materials, particularly Ni–Co, V–Cu and V–Ni, as well as combinations with 4d TMs (Fe–Zr, Fe–Mo, Fe–Ag) and with Mg (Fe–Mg and Ni–Mg). Based on our DFT calculations for each compound, we estimate the volume change during intercalation, the intercalation voltage, the energy density and the thermal stability with respect to reaction with oxygen. Our calculations indicate that the energy density of the binary TM phosphates increases with average band filling while the thermal stability of the compounds decreases.

Towards ab initio screening of co-crystal formation through lattice energy calculations and crystal structure prediction of nicotinamide, isonicotinamide, picolinamide and paracetamol multi-component crystals

Co-crystallisation of a drug with another molecule to form a new crystalline material is an appealing route to enhance physical properties. Despite mounting research effort, there is still considerable uncertainty whether a given co-crystal will form. Previous attempts to use lattice energy calculations to investigate whether a potential co-crystal is thermodynamically more stable than its pure co-former crystals have been inconclusive. In the present study, dispersion-corrected density functional theory is used to minimise the lattice energies of all known co-crystals and salts of nicotinamide, isonicotinamide and picolinamide, and their corresponding neutral co-formers (excluding any organometallic compounds). Out of the resulting 102 co-crystals and salts, 99 (97%) are found to be more stable than their corresponding co-formers. In addition, full crystal structure prediction studies show that two paracetamol co-crystals are very unstable in comparison to their co-formers, thus explaining why these co-crystals have not been observed experimentally. These results demonstrate that a simple yet accurate thermodynamic approach can predict reliably whether a co-crystal can be formed.