II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany.
J Phys Condens Matter. 2011 Nov 9;23(44):445601. doi: 10.1088/0953-8984/23/44/445601. Epub 2011 Oct 18.
Special features of the crystal field splitting of d-levels in the transition metal compounds with small or negative charge-transfer gaps Δ(CT) are considered. We show that in this case the Coulomb term and the covalent contribution to the t(2g)-e(g) splitting have different signs. In order to check theoretical predictions we carried out ab initio band structure calculations for Cs(2)Au(2)Cl(6), in which the charge-transfer gap is negative, so that the d-electrons predominantly occupy low-lying bonding states. For these states the e(g)-levels lie below the t(2g) ones, which demonstrates that at least in this case the influence of the p-d covalency on the total value of the crystal field splitting is stronger than the Coulomb interaction (which would lead to the opposite level order). We also show that the states in the conduction band are made predominantly of p-states of ligands (Cl), with a small admixture of d-states of Au.
本文考虑了电荷转移能隙 Δ(CT)较小或为负的过渡金属化合物中 d 能级的晶体场劈裂的特殊性质。我们表明，在这种情况下，库仑项和共价效应对 t(2g)-e(g)劈裂的贡献具有不同的符号。为了验证理论预测，我们对 Cs(2)Au(2)Cl(6)进行了从头算能带结构计算，其中电荷转移能隙为负值，因此 d 电子主要占据低能成键态。对于这些态，e(g)-能级低于 t(2g)-能级，这表明至少在这种情况下，p-d 共价性对晶体场劈裂的总值的影响强于库仑相互作用（这将导致相反的能级顺序）。我们还表明，导带中的态主要由配体（Cl）的 p 态组成，其中 Au 的 d 态有少量混合。
