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Summary: Where do the H atoms reside in PdHx systems?
RICCARDA CAPUTO1,2
and ALI ALAVI2
*
1
University of Rome `La Sapienza', Physics Department,
P. le A. Moro 5, 00185 Rome, Italy
2
University of Cambridge, Chemistry Department, Lensfield Road,
Cambridge CB2 1EW, UK
(Received 11 December 2002; accepted 22 January 2003)
We present an ab initio density-functional theory study of PdHx systems. We evaluated the
total energy of PdHx systems with the H atoms occupying interstitial (octahedral and
tetrahedral) sites of a Pd supercell, allowing for the relaxation of the coordinates and supercell
dimensions. The majority of our calculations were based on supercells consisting of four Pd
atoms, and up to four H atoms, covering the range from x ¼ 0:25 to x ¼ 1. In addition some
larger calculations are reported. In order to compare the relative stability of systems at
different values of x (at fixed pressure and temperature T ¼ P ¼ 0), we computed the enthalpy
of formation ÁHf ðxÞ of the (non)stoichiometric systems. In the regime x ¼ 0 ! 1, the ÁHf ðxÞ
decrease in a manner indicative of the existence of attractive interactions between the dissolved
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