The increasing use of high-throughput density-functional theory (DFT) calculations in the computational design and optimization of materials requires the availability of a comprehensive set of soft and transferable pseudopotentials. Here we present design criteria and testing results for a new open-source "GBRV" ultrasoft pseudopotential library that has been optimized for use in high-throughput DFT calculations. We benchmark the GBRV potentials, as well as two other pseudopotential sets available in the literature, to all-electron calculations in order to validate their accuracy. The results allow us to draw conclusions about the accuracy of modern pseudopotentials in a variety of chemical environments.Comment: 9 pages, 6 figures, Supplementary information at http://www.physics.rutgers.edu/gbrv/psp_supp.pd

The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We report the results of a community-wide effort that compared 15 solid-state codes, using 40 different potentials or basis set types, to assess the quality of the Perdew-Burke-Ernzerhof equations of state for 71 elemental crystals. We conclude that predictions from recent codes and pseudopotentials agree very well, with pairwise differences that are comparable to those between different high-precision experiments. Older methods, however, have less precise agreement. Our benchmark provides a framework for users and developers to document the precision of new applications and methodological improvements

This review outlines developments in the growth of crystalline oxides on the ubiquitous silicon semiconductor platform. The overall goal of this endeavor is the integration of multifunctional complex oxides with advanced semiconductor technology. Oxide epitaxy in materials systems achieved through conventional deposition techniques is described first, followed by a description of the science and technology of using atomic layer-by-layer deposition with molecular beam epitaxy (MBE) to systematically construct the oxide-silicon interface. An interdisciplinary approach involving MBE, advanced real-space structural characterization, and first-principles theory has led to a detailed understanding of the process by which the interface between crystalline oxides and silicon forms, the resulting structure of the interface, and the link between structure and functionality. Potential applications in electronics and photonics are also discussed.

We argue that various kinds of topological insulators (TIs) can be insightfully characterized by an inspection of the charge centers of the hybrid Wannier functions, defined as the orbitals obtained by carrying out a Wannier transform on the Bloch functions in one dimension while leaving them Bloch-like in the other two. From this procedure, one can obtain the Wannier charge centers (WCCs) and plot them in the two-dimensional projected Brillouin zone. We show that these WCC sheets contain the same kind of topological information as is carried in the surface energy bands, with the crucial advantage that the topological properties of the bulk can be deduced from bulk calculations alone. The distinct topological behaviors of these WCC sheets in trivial, Chern, weak, strong, and crystalline TIs are first illustrated by calculating them for simple tight-binding models. We then present the results of first-principles calculations of the WCC sheets in the trivial insulator Sb2Se3, the weak TI KHgSb, and the strong TI Bi2Se3, confirming the ability of this approach to distinguish between different topological behaviors in an advantageous way.

The Joint Automated Repository for Various Integrated Simulations (JARVIS) is an integrated infrastructure to accelerate materials discovery and design using density functional theory (DFT), classical force-fields (FF), and machine learning (ML) techniques. JARVIS is motivated by the Materials Genome Initiative (MGI) principles of developing open-access databases and tools to reduce the cost and development time of materials discovery, optimization, and deployment. The major features of JARVIS are: JARVIS-DFT, JARVIS-FF, JARVIS-ML, and JARVIS-tools. To date, JARVIS consists of ≈40,000 materials and ≈1 million calculated properties in JARVIS-DFT, ≈500 materials and ≈110 force-fields in JARVIS-FF, and ≈25 ML models for material-property predictions in JARVIS-ML, all of which are continuously expanding. JARVIS-tools provides scripts and workflows for running and analyzing various simulations. We compare our computational data to experiments or high-fidelity computational methods wherever applicable to evaluate error/uncertainty in predictions. In addition to the existing workflows, the infrastructure can support a wide variety of other technologically important applications as part of the data-driven materials design paradigm. The JARVIS datasets and tools are publicly available at the website: https://jarvis.nist.gov.

All known proper ferroelectrics are unable to polarize normal to a surface or interface if the resulting depolarization field is unscreened, but there is no fundamental principle that enforces this behavior. In this work, we introduce hyperferroelectrics, a new class of proper ferroelectrics which polarize even when the depolarization field is unscreened, this condition being equivalent to instability of a longitudinal optic mode in addition to the transverse-optic-mode instability characteristic of proper ferroelectrics. We use first principles calculations to show that several recently discovered hexagonal ferroelectric semiconductors have this property, and we examine its consequences both in the bulk and in a superlattice geometry.Ferroelectrics, which are materials with a non-zero spontaneous polarization that can be switched by an external electric field, have been extensively studied both experimentally and theoretically. Much of the work on ferroelectrics has focused on proper ferroelectrics, such as BaTiO 3 . These have a non-polar reference structure that is related to the ferroelectric ground state by a polar distortion that lowers the energy in zero macroscopic electric field, corresponding to an unstable transverse optic (TO) mode. However, a slab of a typical proper displacive ferroelectric with insulating surfaces will not spontaneously polarize with polarization normal to the surface, because at quadratic order in the polarization the energetic cost of the resulting depolarization field is larger than the energy gain from freezing in the distortion [1]. In order to polarize, the depolarization field must be screened, as for example by a metallic electrode placed on the surfaces of the ferroelectric slab [2].In contrast to proper ferroelectrics, improper ferroelectrics do not have an unstable polar distortion in their high-symmetry structure. Instead, these materials have one or more unstable non-polar distortions. However, when these distortions assume non-zero values they break inversion symmetry in the material, resulting in a nonzero polarization [3][4][5][6]. Because the primary energylowering distortion in an improper ferroelectric is nonpolar, the depolarization field is too weak to prevent the instability. Thus, a slab cut from such a material can develop a non-zero polarization normal to the surface [7].In this work, we demonstrate a new class of "hyperferroelectrics." These are proper ferroelectrics in which the polarization persists in the presence of a depolarization field. Using first-principles calculations, we identify hyperferroelectrics in the recently discovered class of hexagonal ABC semiconducting ferroelectrics [8]. Using first-principles-based modeling, we show that hyperferroelectrics have an electric equation of state that is qualitatively different from those of both proper and improper ferroelectrics, resulting in persistent polarization regardless of screening and unique dielectric behavior.Finally, we discuss the potential applications of hyperferroelectrics, whose abil...

Density functional calculations are performed to investigate the experimentally-reported fieldinduced phase transition in thin-film ZrO2 (J. Müller et al., Nano. Lett. 12, 4318). We find a small energy difference of ∼ 1 meV/f.u. between the nonpolar tetragonal and polar orthorhombic structures, characteristic of antiferroelectricity. The requisite first-order transition between the two phases, which atypically for antiferroelectrics have a group-subgroup relation, results from coupling to other zone-boundary modes, as we show with a Landau-Devonshire model. Tetragonal ZrO2 is thus established as a previously unrecognized lead-free antiferroelectric with excellent dielectric properties and compatibility with silicon. In addition, we demonstrate that a ferroelectric phase of ZrO2 can be stabilized through epitaxial strain, and suggest an alternative stabilization mechanism through continuous substitution of Zr by Hf. [4,5]. Bulk ZrO 2 has a high-symmetry cubic (Fm3m) structure ( Fig. 1(a)) above 2400 K, and a tetragonal (P4 2 /nmc) structure ( Fig. 1(b)) between 2400 K and 1200 K [6]. The tetragonal structure is related to the cubic structure by freezing in an unstable X − 2 mode [7] and is nonpolar. Below 1200 K, ZrO 2 is monoclinic (P2 1 /c) ( Fig. 1(c)). The first-order transition from the tetragonal phase to the monoclinic phase changes the coordination number of Zr from 8 to 7 and increases the volume by ∼ 5 %.In light of the extensive research which has been conducted over the past fifty years on this relatively simple dielectric, the recent report of antiferroelectric-like double-hysteresis loops in thin film ZrO 2 [8] at first seems rather surprising. In thin film ZrO 2 , the tetragonalmonoclinic transition temperature is suppressed and the structure is tetragonal at room temperature [9][10][11]; in contrast, thin film HfO 2 is monoclinic at room temperature and exhibits simple dielectric behavior. The fieldinduced polar phase in ZrO 2 , which appears above a critical field on the order of 2 MV/cm, is isostructural with the ferroelectric phases that have been observed in thin films of [18,19]. The structure of the polar phase is orthorhombic (Pca2 1 ) [20] and corresponds to a distortion of the high-symmetry cubic structure, as depicted in Fig. 1.Antiferroelectrics have recently been the subject of increasing interest [21]. The characteristic electric-fieldinduced transition from a nonpolar to a strongly polar phase is the source of functional properties and promising technological applications. Non-linear strain and dielectric responses due to the phase switching are use- ful for transducers and electro-optic applications [22,23]. The shape of the double hysteresis loop suggests applications in high-energy storage capacitors [24,25]. In addition, an electro-caloric effect can be observed in systems with a large entropy change between the two phases [26]. While most attention has focused on PbZrO 3 and related perovskites [27], a recent theoretical materials design search [28] suggested that there are ma...

We use a first-principles rational-design approach to identify a previously-unrecognized class of ferroelectric materials in the P 63mc LiGaGe structure type. We calculate structural parameters, polarization and ferroelectric well depths both for reported and as-yet hypothetical representatives of this class. Our results provide guidance for the experimental realization and further investigation of high-performance materials suitable for practical applications.A rapidly developing paradigm for the rational design of functional materials is based on the first-principles study of large families of known and as yet unreported compounds. First-principles calculations of structure and properties are used first to explore the microscopic origins and establish design principles for the functional properties of interest, and then to screen a large number of both equilibrium and metastable phases to identify promising candidate systems [1][2][3][4]. One recent study showed the semiconducting members of the ABC half-Heusler family to be piezoelectric, with a range of piezoelectric properties comparable to the much-studied ABO 3 perovskite oxides [4].A ferroelectric is a material with a polar phase produced by a structural transition from a nonpolar highsymmetry paraelectric state, with an electric polarization that can be switched between two or more symmetryrelated variants by application of an electric field [5]. The rational design of new ferroelectric materials is motivated both by fundamental scientific interest and by potential technological applications [6]. New materials can offer better performance, including reduction in switching time, in coercive field and in fatigue, operation at higher or lower temperatures, and the possibility of better integration with other materials based on structural or chemical compatibility. New ferroelectrics with lower band gaps for photoactive applications [7][8][9] are also of interest. Additional practical advantages could include decreased toxicity, for example Pb-free [10], and possible multifunctionality.Any polar structure (if insulating) could potentially support ferroelectricity if the barrier to switching is low enough [11][12][13]. We therefore can search for new ferroelectric semiconductors by targeting intermetallic compounds in polar space groups and screening both reported and hypothetical compounds to find insulating representatives with a low barrier to uniform switching through a nonpolar reference phase, which provides an indication of the barrier to realistic switching. ABC compounds with polar space group P 6 3 mc in the LiGaGe structure type [14][15][16][17] are a promising target class. This structure, shown in Figure 1, is a hexagonal variant of the halfHeusler structure and can be described as a wurtzite structure "stuffed" with a third cation [18]. The Inorganic Crystal Structural Database (ICSD) [19] includes 18 ABC compounds in this structure type that do not contain an f -block element. We can classify these combinations into the following groups: I-III...