Computational study of the structural phases of ZnO
TL;DR: In this article, the structural properties and pressure-induced solid-solid phase transitions of ZnO were investigated using first-principles calculations based on density functional theory, and the B4 phase was found to be the most preferred low-pressure candidate while the B2 phase was favorable at high pressures.
Abstract: We use first-principles calculations based on density functional theory to study the structural properties and pressure-induced solid-solid phase transitions of ZnO. Both the local-density and the generalized gradient approximations are employed together with the projector augmented wave potentials to mimic the electron-ion interaction. We consider the wurtzite (B4), rocksalt (B1), zinc blende (B3), CsCl (B2), NaTl (B32), WC (B${}_{h}$), BN (B${}_{k}$), NiAs (B8${}_{1}$), and AsTi (B${}_{i}$) modifications of ZnO. The calculated structural properties in the B4, B3, B1, and B2 phases are in excellent agreement with earlier ab initiopredictions, as is the transition pressure between them. We find that the B4 phase is the most preferred low-pressure candidate in ZnO while the B2 phase is favorable at high pressures. Apart from the previously reported $B4\ensuremath{\rightarrow}B1\ensuremath{\rightarrow}B2$ phase transition, our study reveals other possible paths for a transition from the B4 to the B2 phase.
Citations
More filters
TL;DR: In this paper, the relative energetic stabilities between the tetrahedrally coordinated (zinc-blende or wurtzite) and octahedral coordinated (rock-salt) phases of MgO, ZnO, GaN, and MnO are obtained by first-principles calculations within the framework of adiabatic connection fluctuation-dissipation theorem (ACFDT) and with the random phase approximation (RPA) to the correlation energy.
Abstract: Accurate relative energetic stabilities between the tetrahedrally coordinated (zinc-blende or wurtzite) and octahedrally coordinated (rock-salt) phases of MgO, ZnO, GaN, and MnO are obtained by first-principles calculations within the framework of adiabatic connection fluctuation-dissipation theorem (ACFDT) and with the random phase approximation (RPA) to the correlation energy. The RPA-ACFDT correctly recovers the rock-salt structure of MnO as the ground-state phase, as observed experimentally, whereas previous density and hybrid functional methods obtained the wrong energy ordering. Even though standard density functionals give the correct ordering of the non-transition-metal compounds, significant quantitative changes occur also for MgO and ZnO. We conclude that the RPA can serve as an important benchmark for structural preferences in polymorphic materials. The present study suggests that density functional predictions for open $d$-shell materials such as transition metal compounds might be more prone to erroneous structure prediction than commonly expected.
50 citations
TL;DR: In this paper, an approach for ab initio many-body calculations of excited states in solids is presented using auxiliary-field quantum Monte Carlo, where an orthogonalization constraint with virtual orbitals is introduced to prevent collapse of the stochastic Slater determinants in the imaginary-time propagation.
Abstract: We present an approach for ab initio many-body calculations of excited states in solids. Using auxiliary-field quantum Monte Carlo, we introduce an orthogonalization constraint with virtual orbitals to prevent collapse of the stochastic Slater determinants in the imaginary-time propagation. Trial wave functions from density-functional calculations are used for the constraints. Detailed band structures can be calculated. Results for standard semiconductors are in good agreement with experiments; comparisons are also made with GW calculations and the connections and differences are discussed. For the challenging ZnO wurtzite structure, we obtain a fundamental band gap of 3.26(16) eV, consistent with experiments.
44 citations
TL;DR: In this paper, a family of ZnkOk (k = 12, 16) cluster-assembled solid phases with novel structures and properties has been characterized utilizing a bottom-up approach with density functional calculations.
Abstract: A family of ZnkOk (k = 12, 16) cluster-assembled solid phases with novel structures and properties has been characterized utilizing a bottom-up approach with density functional calculations. Geometries, stabilities, equation of states, phase transitions, and electronic properties of these ZnO polymorphs have been systematically investigated. First-principles molecular dynamics (FPMD) study of the two selected building blocks, Zn12O12 and Zn16O16, with hollow cage structure and large HOMO–LUMO gap shows that both of them are thermodynamically stable enough to survive up to at least 500 K. Via the coalescence of building blocks, we find that the Zn12O12 cages are able to form eight stable phases by four types of Zn12O12–Zn12O12 interactions, and the Zn16O16 cages can bind into three phases by the Zn16O16–Zn16O16 links of H′, C′, and S′. Among these phases, six ones are reported for the first time. This has greatly extended the family of ZnO nanoporous phases. Notably, some of these phases are even more stab...
39 citations
TL;DR: An extensive survey of (ZnO)N nanostructures ranging from bottom-up generated nanoclusters to top-down nanoparticles cuts from bulk polymorphs, indicating a progressive change in energetic stability from single-layered to multi-layering cage-like nanocluster, and for nanoparticles of around 2.6 nm diameter a transition size is identified.
Abstract: We report on an extensive survey of (ZnO)N nanostructures ranging from bottom-up generated nanoclusters to top-down nanoparticles cuts from bulk polymorphs. The obtained results enable us to follow the energetic preferences of structure and polymorphism in (ZnO)N systems with N varying between 10-1026. This size range encompasses small nanoclusters with 10s of atoms and nanoparticles with 100s of atoms, which we also compare with appropriate bulk limits. In all cases the nanostructures and bulk systems are optimized using accurate all-electron, relativistic density functional theory based calculations with numeric atom centered orbital basis sets. Specifically, sets of five families of (ZnO)N species are considered: single-layered and multi-layered nanocages, and bulk cut nanoparticles from the sodalite (SOD), body centered tetragonal (BCT), and wurtzite (WZ) ZnO polymorphs. Using suitable fits to interpolate and extrapolate these data allows us to assess the size-dependent energetic stabilities of each family. With increasing size our results indicate a progressive change in energetic stability from single-layered to multi-layered cage-like nanoclusters. For nanoparticles of around 2.6 nm diameter we identify a transitional region where multi-layered cages, SOD, and BCT nanostructures are very similar in energetic stability. This transition size also marks the size regime at which bottom-up nanoclusters give way to top-down bulk-cut nanoparticles. Eventually, a final crossover is found where the most stable WZ-ZnO polymorph begins to energetically dominate at N ∼ 2200. This size corresponds to an approximate nanoparticle diameter of 4.7 nm, in line with experiments reporting the observation of wurtzite crystallinity in isolated ligand-free ZnO nanoparticles of 4-5 nm size or larger.
38 citations
TL;DR: In this paper, the prescribed path method is employed to explore transition routes and barriers between even distant minima, suggesting possible transition states and specific transition paths for more detailed analysis, as well as to gain more insights into the temperature dependence of the synthesis and transformation processes in the system.
Abstract: An important issue in modern solid-state chemistry and nanotechnology is the development of a general methodology to predict possible (meta)stable crystalline and nanocrystalline modifications and to study the possible transition routes among them. To analyze the stability of the various potential modifications and study the possible low energy paths among them, the so-called prescribed path method is employed. This method allows us to explore transition routes and barriers between even distant minima, suggesting possible transition states and specific transition paths for more detailed analysis, as well as to gain more insights into the temperature dependence of the synthesis and transformation processes in the system. In this study, we describe and employ the prescribed path method for the example of the energy landscape of ZnO. The focus is on the influence of the temperature on the transformations along the path and on the stability of the various structures in the ZnO system, such as the wurtzite-, t...
32 citations