Ab initio calculations on topological defects in amorphous phosphorus

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Abstract
The structure and dynamic properties of over-coordinated P4 and under-coordinated P2 defects in a-phosphorus are explored using local density functional methods applied to large clusters of phosphorus atoms. The energy levels of the states associated with these defects are found and the structural change on exciting an electron-hole pair are described. The principal conclusions are that VAPS and IVAPS are stable when formed by shearing tubes present in Hittorf's phosphorus; the P2 and P4 defects give rise to vibratory modes around 330 cm-1 and 500 cm-1 respectively and that large Stokes shifts are to be expected since significant structural changes occur upon photoexcitation. This is especially so when an electron is promoted to a P4 state from a P2 state, but less so when it is excited from the valence band.