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The projector augmented-wave ͑PAW͒ method was developed by Blöchl as a method to accurately and efficiently calculate the electronic structure of materials within the framework of density-functional theory. It contains the numerical advantages of pseudopotential calculations while retaining the physics of all-electron calculations, including the correct nodal behavior of the valence-electron wave functions and the ability to include upper core states in addition to valence states in the self-consistent iterations. It uses many of the same ideas developed by Vanderbilt in his ''soft pseudopotential'' formalism and in earlier work by Blöchl in his ''generalized separable potentials,'' and has been successfully demonstrated for several interesting materials. We have developed a version of the PAW formalism for general use in structural and dynamical studies of materials. In the present paper, we investigate the accuracy of this implementation in comparison with corresponding results obtained using pseudopotential and linearized augmented-plane-wave ͑LAPW͒ codes. We present results of calculations for the cohesive energy, equilibrium lattice constant, and bulk modulus for several representative covalent, ionic, and metallic materials including diamond, silicon, SiC, CaF 2 , fcc Ca, and bcc V. With the exception of CaF 2 , for which core-electron polarization effects are important, the structural properties of these materials are represented equally well by the PAW, LAPW, and pseudopotential formalisms. ͓S0163-1829͑97͒00404-9͔

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Using the MoS2‐WTe2 heterostructure as a model system combined with electrochemical microreactors and density function theory calculations, it is shown that heterostructured contacts enhance the hydrogen evolution reaction (HER) activity of monolayer MoS2. Two possible mechanisms are suggested to explain this enhancement: efficient charge injection through large‐area heterojunctions between MoS2 and WTe2 and effective screening of mirror charges due to the semimetallic nature of WTe2. The dielectric screening effect is proven minor, probed by measuring the HER activity of monolayer MoS2 on various support substrates with dielectric constants ranging from 4 to 300. Thus, the enhanced HER is attributed to the increased charge injection into MoS2 through large‐area heterojunctions. Based on this understanding, a MoS2/WTe2 hybrid catalyst is fabricated with an HER overpotential of −140 mV at 10 mA cm−2, a Tafel slope of 40 mV dec−1, and long stability. These results demonstrate the importance of interfacial design in transition metal dichalcogenide HER catalysts. The microreactor platform presents an unambiguous approach to probe interfacial effects in various electrocatalytic reactions.

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Several types of defect structures in PbWO 4 and CaMoO 4 are studied within the framework of density functional theory. While PbWO 4 is currently of greater technological interest, we were able to carry out more extensive calculations for CaMoO 4 , including lattice relaxation, large simulation cells, and more complicated defects. The structural and chemical similarity of the two materials suggests that their defect properties may also be similar. The electronic structure of isolated oxygen vacancies, oxygen and Pb or Ca double vacancies, and substitutional Y are modeled using a supercell approximation. We find that the main effect of oxygen vacancies in PbWO 4 and CaMoO 4 is the introduction of states of W or Mo d character into the band gap. The energies of these defect states are very sensitive to their occupancy. An isolated O vacancy produces a doubly occupied defect state below the conduction band. Removing charge from this defect state lowers its energy and causes additional states of W or Mo d character to move into the band gap. Large supercell simulations for the Ca and O double vacancy in an unrelaxed or slightly relaxed structure produce an unstable electronic structure suggesting the possibility of more extensive lattice distortion. In addition, we also present preliminary results of simulations of interstitial oxygen atoms in CaMoO 4 , finding a relatively stable configuration with the interstitial O forming a weak bond between two MoO 4 clusters.

The projector augmented wave ͑PAW͒ method for electronic structure calculations developed by Blöchl ͓Phys. Rev. B 50, 17 953 ͑1994͔͒ has been very successfully used for density functional studies. It has the numerical advantages of pseudopotential techniques while retaining the physics of all-electron formalisms. We describe a method for generating the set of atom-centered projector and basis functions that are needed for the PAW method. This scheme chooses the shapes of the projector functions from a set of orthogonal polynomials multiplied by a localizing weight factor. Numerical benefits of the scheme result from having direct control of the shape of the projector functions and from the use of a simple repulsive local potential term to eliminate ''ghost state'' problems, which can plague calculations of this kind. Electronic density of states results are presented for the mineral powellite (CaMoO 4). ͓S0163-1829͑98͒03416-X͔

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