We present an update on recently developed methodology and functionality in the computer program LOBSTER (Local Orbital Basis Suite Towards Electronic-Structure Reconstruction) for chemical-bonding analysis in periodic systems. LOBSTER is based on an analytic projection from projector-augmented wave (PAW) densityfunctional theory (DFT) computations [J. Comput. Chem. 2013, 34, 2557, reconstructing chemical information in terms of local, auxiliary atomic orbitals and thereby opening the output of PAW-based DFT codes to chemical interpretation. We demonstrate how LOBSTER has been improved by taking into account time reversal symmetry, thereby speeding up the DFT and LOBSTER calculations by a factor of 2.Over the recent years, the functionalities have also been continually expanded, including accurate projected densities of states (DOS), crystal orbital Hamilton population (COHP) analysis, atomic and orbital charges, gross populations, and the recently introduced ᵈ-dependent COHP. The software is offered free-of-charge for non-commercial research. File list (2)download file view on ChemRxiv Manuscript.pdf (3.50 MiB) download file view on ChemRxiv Supporting_Information.pdf (647.70 KiB)

The crystal orbital bond index (COBI) is a new and intuitive method for quantifying covalent bonding in solid-state materials. COBI is based on the bond index by Wiberg and Mayer and extends their ideas to the case of translationally invariant objects, that is, crystalline matter. COBI’s qualitative interpretation resembles the well-established crystal orbital overlap population and crystal orbital Hamilton population methods but should be more familiar to chemists since it directly relates to the classical bond order. In contrast to the aforementioned descriptors, COBI also allows for examining multicenter interactions within a local-orbital framework. As an additional bonding indicator, we refer to the Ewald sum for electrostatic lattice potentials, thereby enabling the calculation of electrostatic lattice energies as well as site potentials from quantum-mechanical charges as directly derived from the wave function, not from the density.

A robust tool to extract Mulliken and Löwdin charges for (extended) solids from plane waves has been developed and applied.

Solid-state lanthanide (Ln) borides of the simple LnB6 composition not only exhibit exciting physical behavior, in particular magnetic properties, but their electronic structure and chemical bonding are particularly intriguing as well. To shed more light on the latter, we have performed quantum-chemical (DFT+U) electronic-structure calculations and bonding analyses of the entire LnB6 series with Ln from La to Lu. Trivially, the boron framework is held together by the B 2sp orbitals, and this framework bonds to the Ln atoms via covalent–ionic interactions. The Ln 4f electrons, however, are decisive for the magnetic properties. In more detail, the effective charges of the Ln atoms as calculated by (Mulliken or Löwdin) occupation numbers of the 6s/5d/4f orbitals are compatible with experimentally assigned oxidation numbers. The shorter inter-octahedral B–B bonds, dominated by 2s–2p interactions, turn out to be stronger than the intra-octahedral B–B bonding with a more 2p–2p-like character. Interestingly, there are strong structural similarities between the LnB6 motif studied here and gas-phase Ln2B8 species showing inverse sandwich structures, and these similarities are also reflected in the electronic structure. In particular, Ln2B8 is predicted to have a large electron affinity. Hence, this work aims at providing an intrinsic link between gas-phase complexes and solid-state crystal structures in order to better understand the former species.

Identifying strategies for beneficial band engineering is crucial for the optimization of thermoelectric (TE) materials. In this study, we demonstrate the beneficial effects of ionic dopants on n‐type Mg3Sb2. Using the band‐resolved projected crystal orbital Hamilton population, the covalent characters of the bonding between Mg atoms at different sites are observed. By partially substituting the Mg at the octahedral sites with more ionic dopants, such as Ca and Yb, the conduction band minimum (CBM) of Mg3Sb2 is altered to be more anisotropic with an enhanced band degeneracy of 7. The CBM density of states of doped Mg3Sb2 with these dopants is significantly enlarged by band engineering. The improved Seebeck coefficients and power factors, together with the reduced lattice thermal conductivities, imply that the partial introduction of more ionic dopants in Mg3Sb2 is a general solution for its n‐type TE performance. © 2019 Wiley Periodicals, Inc.

Layered phase‐change materials in the Ge−Sb−Te system are widely used in data storage and are the subject of intense research to understand the quantum‐chemical origin of their unique properties. To uncover the nature of the underlying periodic wavefunction, we have studied the interacting atomic orbitals including their phases by means of crystal orbital bond index and fragment crystal orbital analysis. In full accord with findings based on projected force constants, we demonstrate the role of multicenter bonding along straight atomic connectivities. While the resulting multicenter bonding resembles three‐center‐four‐electron bonding in molecules, its solid‐state manifestation leads to distinct long‐range consequences, thus serving to contextualize the material properties usually termed “metavalent”. Eventually we suggest multicenter bonding to be the origin of their astonishing bond‐breaking and phase‐change behavior, as well as the too small “van‐der‐Waals” gaps between individual layers.

We present an update on recently developed methodology and functionality in the computer program LOBSTER (Local Orbital Basis Suite Towards Electronic-Structure Reconstruction) for chemical-bonding analysis in periodic systems. LOBSTER is based on an analytic projection from projector-augmented wave (PAW) densityfunctional theory (DFT) computations [J. Comput. Chem. 2013, 34, 2557], reconstructing chemical information in terms of local, auxiliary atomic orbitals and thereby opening the output of PAW-based DFT codes to chemical interpretation. We demonstrate how LOBSTER has been improved by taking into account time reversal symmetry, thereby speeding up the DFT and LOBSTER calculations by a factor of 2. Over the recent years, the functionalities have also been continually expanded, including accurate projected densities of states (DOS), crystal orbital Hamilton population (COHP) analysis, atomic and orbital charges, gross populations, and the recently introduced 𝒌-dependent COHP. The software is offered free-of-charge for non-commercial research.

Recently, all-optical memory and optical-computation properties of phase-change materials are receiving intensive attention. Because writing/erasing information in these devices is usually achieved by laser pulses, the interaction between the laser and the phase-change materials becomes a key issue for such new applications. In this work, by a time-dependent density-functional theory molecular-dynamics study, the physics underlying the optical excitation induced amorphization of Sc-Sb-Te is revealed, which goes back to superatom-like Sc-centered structural motifs. These motifs are found to be still robust under the excitation. A selected occupation of the Sc d-t 2g orbitals (as a result of optical excitation) leads to a significant change of Sc-centered bond angles. In addition, the especially weak Sb-Te bonds next to the Sc motifs are further diminished by excitations. Therefore, the Sc-centered motifs can promote breaking, switching, and reforming of the surrounding Sb-Te network and, therefore, facilitate the amorphization of Sc-Sb-Te. The study shows the unique role of Sc-centered motifs in optically induced phase transition, and displays potential applications of Sc-Sb-Te alloys in optical memory/computation. npj Computational Materials (2020) 6:31 ; https://doi.