We assess the performance of recent density functionals for the exchange-correlation energy of a nonmolecular solid, by applying accurate calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid metals and nonmetals. The functionals tested are the modified Perdew-Burke-Ernzerhof generalized gradient approximation PBEsol GGA, the second-order GGA SOGGA, and the Armiento-Mattsson 2005 AM05 GGA. For completeness, we also test more standard functionals: the local density approximation, the original PBE GGA, and the Tao-Perdew-Staroverov-Scuseria meta-GGA. We find that the recent density functionals for solids reach a high accuracy for bulk properties lattice constant and bulk modulus. For the cohesive energy, PBE is better than PBEsol overall, as expected, but PBEsol is actually better for the alkali metals and alkali halides. For fair comparison of calculated and experimental results, we consider the zeropoint phonon and finite-temperature effects ignored by many workers. We show how GAUSSIAN basis sets and inaccurate experimental reference data may affect the rating of the quality of the functionals. The results show that PBEsol and AM05 perform somewhat differently from each other for alkali metal, alkaline-earth metal, and alkali halide crystals where the maximum value of the reduced density gradient is about 2, but perform very similarly for most of the other solids where it is often about 1. Our explanation for this is consistent with the importance of exchange-correlation nonlocality in regions of core-valence overlap.

https://dspace.mit.edu/openaccess-disseminate/1721.1/51869

Assessing the performance of recent density functionals for bulk solids

The Na-ion battery is currently the focus of much research interest due to its cost advantages and the relative abundance of sodium as compared to lithium. Olivine NaMPO4 (M = Fe, Fe0.5Mn0.5, Mn) and layered Na2FePO4F are interesting materials that have been reported recently as attractive positive electrodes. Here, we report their Na-ion conduction behavior and intrinsic defect properties using atomistic simulation methods. In the olivines, Na ion migration is essentially restricted to the [010] direction along a curved trajectory, similar to that of LiMPO4, but with a lower migration energy (0.3 eV). However, Na/M antisite defects are also predicted to have a lower formation energy: the higher probability of tunnel occupation with a relatively immobile M2+ cation – along with a greater volume change on redox cycling – contributes to the poor electrochemical performance of the Na-olivine. Na+ ion conduction in Na2FePO4F is predicted to be two-dimensional (2D) in the interlayer plane with a similar low activation energy. The antisite formation energy is slightly higher; furthermore, antisite occupation would not be predicted to impede transport significantly owing to the 2D pathway. This factor, along with the much lower volume change on redox cycling, is undoubtedly responsible for the better electrochemical performance of the layered structure. Where volume change and structural effects do not incur impediments, Na-ion materials may present significant advantages over their Li counterparts.

Na-ion mobility in layered Na2FePO4F and olivine Na[Fe,Mn]PO4

Commercial NMC cells of 18650-type based on a Lix(Ni0.5Mn0.3Co0.2)O2 cathode and a graphitic anode were studied in situ using a combination of high-resolution monochromatic neutron powder diffraction and electrochemical analysis. The structural changes of the electrode materials during cell charge/discharge have been determined using Rietveld refinement and single profile decomposition techniques. A transformation of the graphitic anode to LiC12 and LiC6 through the formation of higher ordered lithium intercalated carbons was observed. A different behavior of electrochemically-driven lattice distortion was observed for NMC material in comparison to LixCoO2 and its influence on the overall cell performance has been discussed in brief. Detailed analysis of the structural changes in the Lix(Ni0.5Mn0.3Co0.2)O2 cathode material revealed reversible Li/Ni cation mixing (5.6(8)%), which is state-of-charge independent below 1600 mAh and vanishing above 1800 mAh (∼0.8Qmax).

Understanding Structural Changes in NMC Li-Ion Cells by In Situ Neutron Diffraction

Contents: 1. Nuclear Power Development. 2. Natural Radioactivity and Radiation Exposures. 3. Neutron Reactions. 4. Nuclear Fission. 5. Chain Reaction and Nuclear Reactors. 6. Types of Nuclear Reactors. 7. Nuclear Fuel Cycle. 8. Nuclear Waste Disposal: Magnitudes of Waste. 9. Storage and Disposal of Nuclear Wastes. 10. Administrative and Policy Issues in Nuclear Waste Disposal. 11. Nuclear Reactor Safety. 12. Nuclear Reactor Accidents. 13. Reactor Safety and Future Nuclear Reactors. 14. Nuclear Energy and Weapons Proliferation. 15. Costs of Electricity from Nuclear Power. 16. The Prospects for Nuclear Power. Appendices.

Nuclear Energy: Principles, Practices, and Prospects

High-throughput computational materials design is an emerging area of materials science. By combining advanced thermodynamic and electronic-structure methods with intelligent data mining and database construction, and exploiting the power of current supercomputer architectures, scientists generate, manage and analyse enormous data repositories for the discovery of novel materials. In this Review we provide a current snapshot of this rapidly evolving field, and highlight the challenges and opportunities that lie ahead.

The high-throughput highway to computational materials design: finding new magnets

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 ...

Crystal Orbital Bond Index: Covalent Bond Orders in Solids

Chemical bonding in main-group IV chalcogenides is an intensely discussed topic, easily understandable because of their remarkable physical properties that predestine these solid-state materials for their widespread use in, for instance, thermoelectrics and phase-change memory applications. The atomistic origin of their unusual property portfolio remains somewhat unclear, however, even though different and sometimes conflicting chemical-bonding concepts have been introduced in the recent years. Here, it is proposed that projecting phononic force-constant tensors for pairs of atoms along differing directions and ranges provide a suitable and quantitative descriptor of the bonding nature for these materials. In combination with orbital-based quantitative measures of covalency such as crystal orbital Hamilton populations (COHP), it is concluded that the well-established many-center and even n-center bonding is an appropriate picture of the underlying quantum-chemical bonding mechanism, supporting the recent proposal of hyperbonded phase-change materials.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.202100163

Long‐Range Forces in Rock‐Salt‐Type Tellurides and How they Mirror the Underlying Chemical Bonding

Future technologies are in need of solid-state materials showing the desired chemical and physical properties, and designing such materials requires a proper understanding of their electronic structures. In this context, recent research on chalcogenides, which were classified as ‘incipient metals’ and included phase-change data storage materials as well as thermoelectrics, revealed a remarkable electronic behavior and possible state (dubbed ‘metavalency’) proposed for the frontier between entire electron localization and delocalization. Because the members of the family of the polar intermetallics vary widely in their properties as well as electronic structures, one may wonder if the aforementioned electronic characteristics are also achieved for certain polar intermetallics. To answer this question, we have employed quantum-chemical tools to examine the electronic structures of the rock salt-type YTe and SnTe belonging to the families of the polar intermetallics and incipient metals, respectively. To justify these classifications and argue as to why an application of the Zintl–Klemm concept (frequently employed to relate the structural features of tellurides to their electronic structures) could be misleading for YTe and SnTe, the electronic structures of YTe and SnTe were first compared to that of the rock salt-type SrTe. In addition, we carried out a Gedankenexperiment by subsequently modifying the chemical composition from YTe to SnTe, and, by doing so, we shed new light on the interdependence between chemical bonding and materials properties. Gradual changes in the former do not necessarily translate into the latter which may undergo discontinuous modifications.

/pdf/bonding-diversity-in-rock-salt-type-tellurides-examining-the-3oagwxoffe.pdf

Bonding diversity in rock salt-type tellurides : examining the interdependence between chemical bonding and materials properties

We present a first-principles study based on plane-wave derived Lowdin population analysis and other local
bonding descriptors to investigate cathode and anode materials for lithium and sodium ion batteries. By comparing the Lowdin charges of common graphite-based anode materials such as LiC6 and LiC12 to other phases such as salts of dicyanamide and nanoporous carbon-based compounds, new conclusions of an improved intercalation behavior of the latter are derived.
In addition, we explore the stability of the dicyanamide salts concerning the removal of Li and Na atoms from the compounds with some of them resulting in dimerized structures. In particular, having a look at the different kinds of bonds and the corresponding covalency indicators reveals new insights into the change of the bonds during dimerization. Considering the generally high thermal stability of metal dicyanamide salts, which are solid at room temperature, their electrochemical activity as well as non-toxicity of alkali metal-based compounds, these materials are potential alternatives to commercially available electrodes, particularly for sodium ion batteries, to pristine graphite-based anode materials.

/pdf/first-principles-plane-wave-based-exploration-of-cathode-and-3whkfgwhbq.pdf

First-Principles Plane-Wave-Based Exploration of Cathode and Anode Materials for Li and Na-ion Batteries

We present a first-principles study based on plane-wave derived Lowdin population analysis and other local bonding descriptors to investigate cathode and anode materials for lithium and sodium ion batteries, with a special emphasis on complex nitrogen chemistry. By comparing the Lowdin charges of commonly used electrode materials to other phases such as salts of dicyanamide and nanoporous carbon-based compounds, new conclusions of an improved intercalation behavior of the latter are derived. In addition, we explore the stability of the dicyanamide salts upon Li and Na removal, some of them resulting in dimerized structures. In particular, having a look at the different kinds of bonds and the corresponding covalency indicators reveals insights into the bonding changes during dimerization. Considering the astonishing thermal stability of metal dicyanamide salts, which are solid at room temperature, their electrochemical activity as well as non toxicity of alkali metal-based compounds, these materials are potential alternatives to commercially available electrodes, particularly as they show some flexibility in exhibiting anodic and cathodic behavior and allow for transition metal-free cathode materials.

/pdf/first-principles-plane-wave-based-exploration-of-cathode-and-21z3jr2iii.pdf

Peter C. Müller

Papers

Crystal Orbital Bond Index: Covalent Bond Orders in Solids

Long‐Range Forces in Rock‐Salt‐Type Tellurides and How they Mirror the Underlying Chemical Bonding

Bonding diversity in rock salt-type tellurides : examining the interdependence between chemical bonding and materials properties

First-Principles Plane-Wave-Based Exploration of Cathode and Anode Materials for Li and Na-ion Batteries

First-Principles Plane-Wave-Based Exploration of Cathode and Anode Materials for Li and Na-ion Batteries involving Complex Nitrogen-based Anions