A theoretical study of the electronic and optical properties of the graphite intercalation compound K(NH3)4C24

被引:2
作者
Bernasconi, L [1 ]
Madden, PA [1 ]
机构
[1] Univ Oxford, Phys & Theoret Chem Lab, Oxford OX1 3QZ, England
关键词
D O I
10.1021/jp020946q
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The electronic properties of the ternary potassium-ammonia graphite intercalation compound K(NH3)(4)C-24 are studied using generalized gradient-corrected density functional theory, following recent theoretical and experimental studies on the microscopic structure and dynamics of intercalation compounds of similar composition. Localized electronic states in the intercalant K-NH3 layer, whose existence has been postulated in order to explain peculiar features in the optical absorption of K(NH3)(x)C-24 compounds, with x similar or equal to 4 and, ultimately, the occurrence of a 2D metal-nonmetal transition at x similar or equal to 4.3, are shown to originate from the overlap of diffuse K-NH3 hybrid orbitals enveloping discrete K(NH3)(4) clusters. This gives rise to a highly inhomogeneous conduction band extending in the inter-cluster region, which percolates throughout the crystal in narrow winding channels bounded by H atoms. The estimated frequency-dependent complex dielectric function is found to reproduce with remarkable accuracy the experimental spectra. In particular, we can establish a direct link between the intercalate state and the occurrence of the 1.85 eV peak in the epsilon(2)(omega) spectrum, a well-known feature specific to K-NH3 graphite intercalation compounds. Issues related to the actual occupation of the intercalate state (depending on the degree of charge back-transfer from the C sheets to the K-NH3 intercalate) are discussed within the limitations of a conventional electronic structure density functional approach.
引用
收藏
页码:12916 / 12928
页数:13
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