Unconventional materials:the mismatch between electronic charge centers and atomic positions

非常规材料:电子分布不在原子上

The complete band representations(BRs)have been constructed in the work of topological quantum chemistry.Each BR is expressed by either a localized orbital at a Wyckoff site in real space,or by a set of irreducible representations in momentum space.In this work,we define unconventional materials with a common feature of the mismatch between average electronic centers and atomic positions.They can be effectively diagnosed as whose occupied bands can be expressed as a sum of elementary BRs(eBRs),but not a sum of atomic-orbital-induced BRs(aBRs).The existence of an essential BR at an empty site is described by nonzero real-space invariants(RSIs).The"valence"states can be derived by the aBR decomposition,and unconventional materials are supposed to have an uncompensated total"valence"state.The high-throughput screening for unconventional materials has been performed through the first-principles calculations.We have discovered 423 unconventional compounds,including thermoelectronic materials,higher-order topological insulators,electrides,hydrogen storage materials,hydrogen evolution reaction electrocatalysts,electrodes,and superconductors.The diversity of these interesting properties and applications would be widely studied in the future.

在拓扑量子化学中,研究人员发展了空间群下完备的基本能带表示,既对应于实空间的局域轨道,又对应于倒空间的一组不可约表示.通过计算实际材料的高对称k点的不可约表示,再利用基本能带表示分解来判断材料的拓扑性质.本研究发现拓扑平庸的材料可以分为电子电荷中心在原子上的常规材料和电荷中心不在原子上的“非常规材料”.这种非常规的电子分布特征在特定晶体对称群下可以方便地由能带表示分解来判断:占据态是基础能带表示的组合,但不是原子轨道对应的能带表示的组合.同时作者引入空位上的(必要)能带表示和实空间不变量来标定这一非常规电子分布特性.利用这一基于对称性本征值的能带表示分解方法,本文通过高通量搜索找到了423个非常规材料,并讨论了这些材料热电、储氢、催化、超导等特殊的化学性质与非常规电荷分布的相关性.