This work assesses the Heyd-Scuseria-Ernzerhof (HSE) screened Coulomb hybrid density functional for the prediction of lattice constants and band gaps using a set of 40 simple and binary semiconductors. An extensive analysis of both basis set and relativistic effects is given. Results are compared with established pure density functionals. For lattice constants, HSE outperforms local spin-density approximation (LSDA) with a mean absolute error (MAE) of 0.037 A for HSE vs 0.047 A for LSDA. For this specific test set, all pure functionals tested produce MAEs for band gaps of 1.0-1.3 eV, consistent with the very well-known fact that pure functionals severely underestimate this property. On the other hand, HSE yields a MAE smaller than 0.3 eV. Importantly, HSE correctly predicts semiconducting behavior in systems where pure functionals erroneously predict a metal, such as, for instance, Ge. The short-range nature of the exchange integrals involved in HSE calculations makes their computation notably faster than regular hybrid functionals. The current results, paired with earlier work, suggest that HSE is a fast and accurate alternative to established density functionals, especially for solid state calculations.

We present a novel comprehensive first-principles theoretical study of the electronic properties and relative stabilities of edge-oxidized zigzag graphene nanoribbons. The oxidation schemes considered include hydroxyl, carboxyl, ether, and ketone groups. Using screened exchange density functional theory, we show that these oxidized ribbons are more stable than hydrogen-terminated nanoribbons except for the case of the etheric groups. The stable oxidized configurations maintain a spin-polarized ground state with antiferromagnetic ordering localized at the edges, similar to the fully hydrogenated counterparts. More important, edge oxidation is found to lower the onset electric field required to induce half-metallic behavior and extend the overall field range at which the systems remain half-metallic. Once the half-metallic state is reached, further increase of the external electric field intensity produces a rapid decrease in the spin magnetization up to a point where the magnetization is quenched completely. Finally, we find that oxygen containing edge groups have a minor effect on the energy difference between the antiferromagnetic ground state and the above-lying ferromagnetic state.

We present theoretical evidence, based on total-energy first-principles calculations, of the existence of spin-polarized states well localized at and extended along the edges of bare zigzag boron nitride nanoribbons.Our calculations predict that all the magnetic configurations studied in this work are thermally accessible at room temperature and present an energy gap. In particular, we show that the high spin state, with a magnetic moment of 1 µ B at each edge atom, presents a rich spectrum of electronic behaviors as it can be controlled by applying an external electric field in order to obtain metallic ↔ semiconducting ↔ halfmetallic transitions.

We analyze the relevance of finite-size effects to the electronic structure of long graphene nanoribbons using a divide and conquer density functional approach. We find that for hydrogen terminated graphene nanoribbons most of the physical features appearing in the density of states of an infinite graphene nanoribbon are recovered at a length of 40 nm. Nevertheless, even for the longest systems considered (72 nm long) pronounced edge effects appear in the vicinity of the Fermi energy. The weight of these edge states scales inversely with the length of the ribbon and they are expected to become negligible only at ribbons lengths of the order of micrometers. Our results indicate that careful consideration of finite-size and edge effects should be applied when designing new nanoelectronic devices based on graphene nanoribbons. These conclusions are expected to hold for other one-dimensional systems such as carbon nanotubes, conducting polymers, and DNA molecules.Graphene nanoribbons (GNRs) have been suggested as potential candidates for replacing electronic components and interconnects in future nanoelectronic 1,2,3,4,5,6,7 and nanospintronic 8,9,10 devices. Experiments have revealed the possibility of obtaining a wide range of electronic behavior when studying these systems, ranging from coherent transport 11 suitable for interconnects, to field effect switching capabilities 12 needed for electronic components design. While many transport experiments involve long segments of GNRs 1,11,13,14 , recent developments have allowed the fabrication of graphene based quantum dots 5,7,15,16 . The reduced dimension of these quantum dots introduces important physical phenomena such as quantum confinement and edge effects. 10,17,18,19,20,21,22,23 Several theoretical studies have emphasized the importance of such effects when considering the electronic structure, 24,25,26,27,28 electric transport, 29,30,31,32,33 and magnetic 34,35,36 properties of finite carbon nanotubes (CNTs). These effects are expected to be manifested in experiments involving the dielectric screening constants, 26 optical excitations 37 and Raman spectrum 38 of such systems. Similar to CNTs it is predicted that the physical characteristics of finite GNRs may be considerably different from those of their infinite counterparts. Therefore, it is essential to identify the limit at which finite-size effects have to be taken into account. An important question therefore arises: what is the length at which a finite GNR becomes indistinguishable from its infinite counterpart?The purpose of this Letter is to provide a quantitative answer to this question based on first-principles calculations. To this end, we employ density functional theory (DFT) to study the electronic structure of hydrogen terminated GNRs as a function of their length, up to 72 nm. Finite-size effects are studied using a divide and conquer approach for first-principles electronic structure and transport calculations through finite elongated systems. 39 A careful comparison with the electronic st...

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