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First-principles calculations within the density-functional theory have been performed for a 3,4,9,10 perylenetetracarboxylic dianhydride ͑PTCDA͒ molecule deposited on Al͑111͒ and Ag͑111͒ substrates, focusing on the structural and electronic properties. The relatively large interplanar distance between the PTCDA plane and the Al surface, along with the small adsorption energy, suggest the interaction to be pretty weak. Moreover, the analysis of Mulliken population combined with the density of states shows that the main interactions occur in the molecular anhydride end groups, whereas the perylene core is basically unaffected by the Al substrate. Very similar results are obtained for PTCDA deposited on the Ag͑111͒ surface, the interaction being even weaker than with Al, as expected for the less reactive noble metal. As for the technologically important issue of the potential lineup, our results show that the PTCDA/Al contact has a rectifying character, with a p-type Schottky barrier height of about 1.5 eV. This same value is obtained for the PTCDA/Ag contact, irrespective of the interface geometry. This suggests that, irrespective of the underlying metal, the Fermi level is pinned at the same energy position with respect to the PTCDA highest occupied molecular orbital, in excellent qualitative agreement with experimental findings.

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Abstract. -We study the influence of structural lattice fluctuations on the elastic electron transport in single-wall carbon nanotubes within a density-functional-based scheme. In the linear response regime, the linear conductance is calculated via configurational averages over the distorted lattice. Results obtained from a frozen-phonon approach as well as from molecular dynamics simulations are compared. We further suggest that the effect of structural fluctuations can be qualitatively captured by the Anderson model with bond disorder. The influence of individual vibrational modes on the electronic transport is discussed as well as the role of zero-point fluctuations.Introduction. -Carbon nanotubes (CNTs) have become a paradigm in the physics of low-dimensional systems due to their fascinating properties [1]. Especially, the close interconnection between their chirality and their electronic structure make them an ideal candidate for applications in the field of molecular electronics. As a consequence, extensive experimental and theoretical research has been carried out in the past years to clarify their structural and conducting properties [1].Concerning quantum transport in CNTs, it is theoretically well-established that the linear conductance is quantized in units of. In the case of metallic tubes, effective low-energy theories as well as tight-binding and ab initio calculations have demonstrated that two massless electronic bands with linear dispersion cross the Fermi points at K(K ′ ) = +(−)2π/3a 0 , a 0 being the CNT lattice constant [1,2]. As a result, two transport channels per spin are open at the Fermi level E F , leading to a conductance of 4×G 0 . This value is conserved even in the presence of disorder as far as the range of the impurity potential is larger than the nanotube lattice constant [3]. The same is expected to hold in the presence of vibrations

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