多铁材料BaCoF$lt;sub$gt;4$lt;/sub$gt;电子结构的第一性原理研究

采用基于密度泛函理论的广义梯度近似方法和赝势平面波法，对多铁材料BaCoF₄的铁电反铁磁相和可能的顺电相的电子结构进行了第一性原理研究.研究表明，反铁磁态很可能有利于低温下的铁电稳定性，F的强负电性使得体系内原子间主要是离子键相互作用.Co离子与在bc面上的F（2），F（3）离子间完全是离子键作用，而与F（4）间有较弱的共价作用，与F（1）间作用介于两者之间.铁电畸变主要来源于Ba离子与F（1）, F（2）, F（3）离子沿着c轴方向的相对位移，F（4）对铁电性的贡献最少.铁电相中F（2）, F（3）离子的能量低于中心对称相，最大位移贡献者F（1）的化学键性由弱共价作用到离子键的变化也是最大的，这均有利于体系的稳定. 关键词： 第一性原理 铁电性 铁电畸变 反铁磁性

First-principles investigation of the electronic properties of multiferroic BaCoF4

The electronic properties of multiferroic BaCoF₄ with ferroelectric antiferromagnetic phase and paraelectric phase are calculated using density functional theory with spin-polarized generalized-gradient approximation and plane wave pseudopotentials. It is found that anti-ferromagneticism probably favors to the ferroelectric stability at low temperature and the ion bond interaction is the main interation in the BaCoF₄ system due to the strong electronegativity of F atoms. As to the CoF₆ octahedron, there is entirely ionic bond between Co ion and F（2） or F（3） ions （bc plane）, but weak covalent bond between Co ion and F（1） ion and still weaker for F（4） ion. The ferroelectric distortion is only induced by relative displacement of Ba ion and F ion along c axis, and F（4） displacement contributes least to ferroelectric phase transformation . In addition, the energy of s and p orbitals of F（2） or F（3） ion is lower in the ferroelectric phase than in the centor-symmetric phase and the covalence character of F（1） ion, whose contribution to the displacement is the largest, is almost lost, which stabilizes the structure of the ferroelectric system.