Molybdenite (MoS2) undergoes a transition from an indirect to direct gap semiconductor exhibiting strong photoluminescence when confined in a 2D monolayer. We investigate the effect of interlayer interactions on the band structure and density of states using the screened hybrid functional of Heyd, Scuseria, and Ernzerhof. We show that for the bulk and monolayer systems, our short-range screened hybrid functional produces band gaps in good agreement with experiment. Our functional includes only interlayer interactions of non-van der Waals origin, predicts properties consistent with recent experiments, and provides predictions for few-layered systems.

We present a multistep method combining multispectroscopic experiments with DFT calculations to determine the complete Al distribution in silicon-rich zeolites, independent of the presence of AlÀOÀ(SiÀO) n ÀAl (n = 1, 2) sequences in their frameworks. 29 Si MAS NMR spectroscopy is employed to confirm the absence of AlÀOÀSiÀOÀAl in the framework of silicon-rich zeolites while 27 Al 3Q MAS NMR spectroscopy and DFT computations of 27 Al isotropic chemical shifts serve to determine the locations of isolated Al atoms. The maximum ion-exchange capacity of zeolites for [Co 2þ (H 2 O) 6 ] 2þ reveals the presence of close Al atoms (i.e., those Al atoms which are able to balance [Co 2þ (H 2 O) 6 ] 2þ ions). Then visible spectroscopy of the bare Co(II) ion in the dehydrated zeolite of the samples with close Al is utilized to identify the locations of the corresponding AlÀOÀ(SiÀO) 2 ÀAl pairs in a ring. Subsequently, their 27 Al isotropic chemical shifts are evaluated at DFT and the complete Al distribution is determined. The complete Al siting in three ferrierite samples with only isolated framework Al atoms and two ferrierites with AlÀOÀ(SiÀO) 2 ÀAl sequences was determined. Our results reveal that the Al siting in the former samples varies with the conditions of the zeolite synthesis; Al is present in three or four sites (T1b, T2, T3, and T4) depending on the sample while T1a is never occupied by Al and the concentrations of Al atoms in various T sites are very diverse. For ferrierites with both isolated and close Al atoms, isolated Al atoms occupy the T2, T3, and T4 sites and the close Al atoms are arranged in Al(T1a)ÀOÀ(SiÀO) 2 ÀAl(T1a) and Al(T2)ÀOÀ(SiÀO) 2 ÀAl(T2) sequences forming the R and β À 2 cationic sites, respectively. Isolated Al atoms do not occupy the T1b site and close Al atoms do not form Al(T4)ÀOÀ(SiÀO) 2 À Al(T4) sequences of the β À 1 site. The differences between the concentrations of Al in T sites are not as pronounced as those for the ferrierite samples with only isolated framework Al atoms. In addition, our results reveal that the Al siting in ferrierite is not random and depends on the conditions of the zeolite synthesis.

We show that the middle-range exchange-correlation hybrid of Henderson, Izmaylov, Scuseria and Savin (HISS) performs extremely well for elemental and binary semiconductors with narrow or visible spectrum band gaps, as well as some wider gap or more ionic systems used commercially. The lattice parameters are superior to those predicted by the screened hybrid functional of Heyd, Scuseria and Ernzerhof (HSE), and provide a significant improvement over geometries predicted by semilocal functionals. HISS also yields band gaps superior to those produced by functionals developed specifically for the solid state. Timings indicate that HISS is more computationally efficient than HSE, implying that the high quality lattice constants coupled with improved optical band gap predictions render HISS a useful adjunct to HSE in the modeling of geometry-sensitive semiconductors.PACS numbers: 71.15.m 71.15.Mb, 71.20.b, 71.20.Nr, 71.28+d, 71.45.Gm, 2

We have investigated the structural phase transitions of the transition metal oxide perovskites SrTiO 3 , LaAlO 3 , and LaTiO 3 using the screened hybrid density functional of Heyd, Scuseria, and Ernzerhof (HSE06). We show that HSE06-computed lattice parameters, octahedral tilts, and rotations, as well as electronic properties, are significantly improved over semilocal functionals. We predict the crystal-field splitting ( CF ) resulting from the structural phase transition in SrTiO 3 and LaAlO 3 to be 3 meV and 10 meV, respectively, in excellent agreement with experimental results. HSE06 identifies correctly LaTiO 3 in the magnetic states as a Mott insulator. Also, it predicts that the GdFeO 3 -type distortion in nonmagnetic LaTiO 3 will induce a large CF of 410 meV. This large crystal-field splitting associated with the large magnetic moment found in the G-type antiferromagnetic state suggests that LaTiO 3 has an induced orbital order, which is confirmed by the visualization of the highest occupied orbitals. These results strongly indicate that HSE06 is capable of efficiently and accurately modeling perovskite oxides and promises to efficiently capture the physics at their heterointerfaces.

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