Electronic nematicity is an important order in most iron-based superconductors, and FeSe represents a special example, in which nematicity disentangles from spin ordering. A first-principle description of this order remains elusive. Here, we show that by carefully searching the paramagnetic energy landscape within the density functional theory, a nematic solution stands out at either the +U or hybrid functional level with the lowest energy. The band structure and Fermi surface can be well compared with the recent experimental results. Symmetry analysis assigns the dominant order parameter to the E_u irreducible representations of the D_4h point group. Distinct from the B_1g Ising nematicity as widely discussed in the context of vestigial stripe antiferromagnetic order, the two-component E_u vector order features mixing of the Fe d-orbitals and inversion symmetry breaking, which lead to striking experimental consequences, e.g., missing of an electron pocket.

在大多数铁基超导体中，电子向列性是一个重要的顺序，而FeSe代表一个特殊的例子，其中向列性与自旋有序分离。对该顺序的第一原理描述仍然难以捉摸。在这里，我们表明，通过在密度泛函理论中仔细搜索顺磁能量分布，向列解在+ U或混合函数级具有最低的能量。能带结构和费米表面可以很好地与最近的实验结果进行比较。对称性分析将主导顺序参数分配给D _4h点组的E _u不可约表示。与B _1g不同由于在残留条带反铁磁有序情况下广泛讨论的向列性，两组分E _u向量有序特征是Fe d轨道的混合和对称反转的破坏，这会导致惊人的实验结果，例如缺少电子口袋。