Ab Initio and First Principles Studies of Halide Perovskites

Even, Jacky; Katan, Claudine

doi:10.1002/9783527800766.ch1_02

Cited by 3 publications

(4 citation statements)

References 92 publications

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“…Also, our big supercell cannot be called monomorphous: the latter is a single motif, not a single unit cell). Our finding suggests that the widely discussed single formula unit cubic Pm-3m structure of halide perovskites 4,10,[13][14][15][16][17][18][19][20][21][22][23][24] does not really exist, except as a macroscopically averaged fictitious structural model. Because X-ray diffraction has a rather long coherence length, such polymorphous systems were often fit in structure refinement models 11,25 by a macroscopically averaged ("fictitious monomorphous") cubic Pm-3m unit cells.…”

Section: Introductionmentioning

confidence: 85%

“…Because X-ray diffraction has a rather long coherence length, such polymorphous systems were often fit in structure refinement models 11,25 by a macroscopically averaged ("fictitious monomorphous") cubic Pm-3m unit cells. Standard electronic structure calculations 4,10,[13][14][15][16][17][18][19][20][21][22][23][24] that use input structures directly from crystal databases often modeled the properties of the system (band gaps, absorption spectra, thermodynamic stability, alloy mixing enthalpies) as the property <P>=P(S0) of the reported macroscopically averaged monomorphous structure 26,27 S0 rather than the average Pobs=ΣP(Si) of the properties {P(Si)} of the individual, low symmetry microscopic configurations {Si ; i=1, N}.…”

Section: Introductionmentioning

confidence: 99%

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Polymorphous nature of cubic halide perovskites

et al. 2020

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It has been long known that numerous halide and oxide perovskites can have non-ideal octahedra, showing tilting, rotation, and metal atom displacements. It has also been known that compounds that have at low temperatures a single structural motif ("monomorphous structures") could become disordered at higher temperatures, resulting in non-ideal octahedra as an entropy effect. What is shown here is that in many cubic halide perovskites and some oxides compounds a distribution of different low-symmetry octahedra ("polymorphous networks") emerge already from the minimization of the systems internal energy, i.e., they represent the intrinsic, preferred low temperature pattern of chemical bonding. Thermal disorder effects build up at elevated temperatures on top of such low temperature polymorphous networks. Compared with the monomorphous counterparts, the polymorphous networks have lower predicted total energies (enhanced stability), larger band gaps and dielectric constants now dominated by the ionic part, and agrees much more closely with the observed pair distribution functions. The nominal cubic perovskites (Pm-3m) structure deduced from X-Ray diffraction is actually a macroscopically averaged, high symmetry configuration, which should not be used to model electronic properties, given that the latter reflect a low symmetry local configuration.

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Section: Introductionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Polymorphous nature of cubic halide perovskites

et al. 2020

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“…But this requires that we allow a larger than minimal unit cell, so that rotations can be accommodated geometrically. However, it is often assumed [38,[68][69][70] that the electronic structure of cubic phase of lead (tin) halide perovskite can be represented within a single-cell cubic (𝑃𝑚3 ̅ 𝑚) model (monomorphous models), as shown in Figure 7(a). Restricted by the small size and periodic boundary condition, such structure cannot accommodate rotations (as shown by the blue lines in Figure 7(b)).…”

Section: Full Supercell Calculation Of Rotation-induced Mass Enhancem...mentioning

confidence: 99%

Mass enhancement in 3d and s−p perovskites from symmetry breaking

et al. 2021

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In some d-electron oxides the measured effective mass 𝑚 exptl * has long been known to be significantly larger than the model effective mass 𝑚 model * deduced from mean-field band theory, i.e., 𝑚 exptl * = 𝛽𝑚 model * , where 𝛽 > 1 is the 'mass enhancement', or 'mass renormalization' factor. Previous applications of density functional theory (DFT), based on the smallest number of possible magnetic, orbital, and structural degrees of freedom, missed such mass enhancement, a fact that was taken as evidence of strong electronic correlation. The current paper reports in a range of d-electron perovskites SrVO3, SrTiO3, BaTiO3 and LaMnO3 as well as p-electron perovskites CsPbI3 and SrBiO3 that the symmetry-breaking spin and structural effects included in DFT captures already the magnitudes and trends in mass enhancement for both electrons and holes, but only when enlarged unit cells, which are large enough to allow for symmetry breaking distortions and concomitant variations in spin order, are explored for their ability to lower the total energy. The paper analyzes the different symmetry breaking modalities contributing to mass enhancement, finding common effects in range of d-as well as p-electron perovskites. * , where 𝛽 is the 'mass enhancement', or 'mass renormalization' factor. Effective masses 𝑚 exptl * are generally deduced from experiment via model assumptions (such as band parabolicity or various averages over the mass tensor), leading to different effective mass definitions in different experiments, including the mass 𝑚 * ∝ 1 𝑣 𝐹 ⁄ , deduced from Fermi-velocity (𝑣 𝐹 ), or from density of states (DOS) 𝑚 * ∝ (𝐷(𝐸)) 2 3 ⁄ , from specific-heat coefficient 𝑚 * ∝ 𝛾, from magnetic susceptibility 𝜒 ∝ 𝑚 * (1 − 𝑚 0 2 3𝑚 * 2 ), and from bandwidth 𝑊 ∝ 1 𝑚 * ⁄ . Values of 𝛽 > 1 were reported in the * were compared with theoretical values 𝛽(Theory: model) = 𝑚 Theory * /𝑚 model * obtained from advanced theory (such as dynamic mean-field theory, DMFT [13-23]). Because 𝑚 model * is obtained from mean-field band theory, the predicted theoretical enhancement 𝛽(Theory: model) > 1 has been interpreted to be due to strong correlation effects [13-23]. For example, in DMFT, wavefunction localizes and bandwidth narrows (thus leading to mass enhancement) due to pure electronic symmetry breaking [15,24] induced by the dynamic self-energy from the impurity atom embedded in a mean-field bath. Finding for a compound that 𝛽(DMFT: model) > 1 consistent with 𝛽(exptl: model) > 1 helped classify the pertinent compounds as being highly correlated. This line of thinking, however, does not consider the possibility that sources of mass enhancement other than symmetry-preserving correlation might exist. The model calculations used to extract 𝑚 model * have invariably been [13-23] rather naïve (N) level of density functional theory (N-DFT), based on the least number of possible magnetic, orbital and structural degrees of freedom. Indeed, they have assumed one or a few of the following approximations: A highly symmetric unit cell symmetry (e.g., 𝑃𝑚3 ̅...

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“…On the theoretical side, Kohn-Sham (KS) density functional theory (DFT), 13,14 within the local density approximation (LDA) 14 or the generalized gradient approximation (GGA), 15,16 has been widely used to study the optoelectronic properties of hybrid halide perovskites and has proved to be efficient to compute materials structure-property relationships at a reasonable computational cost 17,18 . However, it is well known that the standard LDA and GGA are not appropriate to compute the band gap since giving too small band gaps or even a wrong metallic behavior rather than an insulating one in some cases (see, e.g., refs 19 and 20).…”

Section: Introductionmentioning

confidence: 99%

Efficient and accurate calculation of band gaps of halide perovskites with the Tran-Blaha modified Becke-Johnson potential

et al. 2019

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We report on a reoptimization of the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential dedicated to the prediction of the band gaps of 3-dimensional (3D) and layered hybrid organicinorganic perovskites (HOP) within pseudopotential-based density functional theory methods. These materials hold promise for future photovoltaic and optoelectronic applications. We begin by determining a set of parameters for 3D HOP optimized over a large range of materials. Then we consider the case of layered HOP. We design an empirical relationship that facilitates the prediction of band gaps of layered HOP with arbitrary interlayer molecular spacers with a computational cost considerably lower than more advanced methods like hybrid functionals or GW. Our study also shows that substituting interlayer molecular chains of layered HOP with Cs atoms is an appealing and cost-effective route to band gap calculations. Finally, we discuss on the pitfalls and limitations of TB-mBJ for HOP, notably its tendency to overestimate the effective masses due to the narrowing of the band dispersions. We expect our results to extend the use of TB-mBJ for other low-dimensional materials. 2 B. Traore et coll. Phys. Rev.

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Ab Initio and First Principles Studies of Halide Perovskites

Cited by 3 publications

References 92 publications

Polymorphous nature of cubic halide perovskites

Polymorphous nature of cubic halide perovskites

Mass enhancement in 3d and s−p perovskites from symmetry breaking

Efficient and accurate calculation of band gaps of halide perovskites with the Tran-Blaha modified Becke-Johnson potential

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