We review the GPAW open-source Python package for electronic structure calculations. GPAW is based on the projector-augmented wave method and can solve the self-consistent density functional theory (DFT) equations using three different wave-function representations, namely real-space grids, plane waves, and numerical atomic orbitals. The three representations are complementary and mutually independent and can be connected by transformations via the real-space grid. This multi-basis feature renders GPAW highly versatile and unique among similar codes. By virtue of its modular structure, the GPAW code constitutes an ideal platform for the implementation of new features and methodologies. Moreover, it is well integrated with the Atomic Simulation Environment (ASE), providing a flexible and dynamic user interface. In addition to ground-state DFT calculations, GPAW supports many-body GW band structures, optical excitations from the Bethe-Salpeter Equation, variational calculations of excited states in molecules and solids via direct optimization, and real-time propagation of the Kohn-Sham equations within time-dependent DFT. A range of more advanced methods to describe magnetic excitations and non-collinear magnetism in solids are also now available. In addition, GPAW can calculate non-linear optical tensors of solids, charged crystal point defects, and much more. Recently, support for graphics processing unit (GPU) acceleration has been achieved with minor modifications to the GPAW code thanks to the CuPy library. We end the review with an outlook, describing some future plans for GPAW.
Discovery of high-performance materials remains one of the most active areas in photovoltaics (PV) research. Indirect band gap materials form the largest part of the semiconductor chemical space, but predicting their suitability for PV applications from first-principles calculations remains challenging. Here, we propose a computationally efficient method to account for phonon-assisted absorption across the indirect band gap and use it to screen 127 experimentally known binary semiconductors for their potential as thin-film PV absorbers. Using screening descriptors for absorption, carrier transport, and nonradiative recombination, we identify 28 potential candidate materials. The list, which contains 20 indirect band gap semiconductors, comprises well-established (3), emerging (16), and previously unexplored (9) absorber materials. Most of the new compounds are anion-rich chalcogenides (TiS3 and Ga2Te5) and phosphides (PdP2, CdP4, MgP4, and BaP3) containing homoelemental bonds and represent a new frontier in PV materials research. Our work highlights the previously underexplored potential of indirect band gap materials for optoelectronic thin-film technologies.
We have systematically investigated a family of newly proposed two-dimensional MA2N4 materials (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; A = Si, Ge) using first-principles calculation. We categorize the potential of these materials into three different applications based on accurate simulation of band gap (using Hybrid HSE06 functional) and the associated descriptors. Three candidate materials (MoGe2N4, HfSi2N4, and NbSi2N4) turn out to be extremely promising for three different applications. MoGe2N4 and HfSi2N4 monolayers show strong optical absorption in the visible range, including high transition probability from the valence to conduction band. The GW+BSE calculations confirm a strong excitonic effect in both the systems. With a band gap of 1.42 eV, multilayer MoGe2N4 shows reasonably large simulated efficiency (â¼15.40%) and hence can be explored for possible photovoltaic applications. High optical absorption, suitable band gap/edge positions, and the CO2 activation make HfSi2N4 monolayer a promising candidate for photocatalytic CO2 reduction. NbSi2N4, on the other hand, belongs to a new class of spintronic material called a bipolar magnetic semiconductor, recommended for spin-transport-based applications.
Half-Heusler (HH) alloys provide a general platform for searching candidate materials for various energy applications. Here, we present a high-throughput first-principles calculation of a set of 960 eight valence-electron HH alloys to search potential candidates for thermoelectric (TE), solar harvesting (SH), topological insulator (TI), and transparent conductor (TC) applications. The initial screening parameters (such as stability, bandgap (Eg), band-inversion strength) followed by application specific descriptors are used to predict promising compounds. 121 out of 960 compounds were found to be dynamically and chemically stable. Of them, 31 compounds (with Eg < 1.5 eV) were studied for TE application, 30 (with 1 < Eg < 1.8 eV) for SH application, 21 for TI application, and 29 (with Eg > 2 eV) for TC applications. Some of the compounds show reasonably high thermoelectric figure of merit (ZT â¼ 1.6) and solar efficiency (SLME) > 20%, comparable to existing state-of-the-art materials. Surface band structure and topological Z2 index reconfirms the robustness of topological behavior. We strongly believe that our calculations should leverage useful insights to experimentalists.
Recently, oxide perovskites are garnering tremendous attention from the scientific community as possible alternatives to the currently used active materials in photovoltaic (PV) and photoelectrochemical (PEC) devices. Herein, we report the stability and promising optoelectronic properties of a few previously unexplored periodates A2BIO6 (A = alkali metal; B = Bi, Sb, In, Tl, Ga). Our compositional phase diagram analysis reveals two compounds Na2BIO6 (B = Bi, In) that stabilize in monoclinic phase at thermodynamic equilibrium, showing band gaps (Eg) in the visible region. Band engineering via alloying Bi in Na2InIO6 introduces Bi 6s lone pair bands above the valence band maxima (VBM), while alloying Tl in Na2BiIO6 introduces an intermediate band (Tl s character) below the conduction band minima. These alloys, Na2Bi0.25In0.75IO6 and Na2Tl0.25Bi0.75IO6, acquire Eg's of 1.66 and 1.78 eV, respectively. Apart from band gap, the antibonding VBM, favorable optical absorption, highly dispersive band edges, and well-positioned VBM (for efficient oxygen evolution reaction) make these compounds highly promising for PV and PEC applications.
Recently, lead free all-inorganic double perovskites have revolutionized photovoltaic research, showing promising light emitting efficiency and tunability via modification of inherent structural and chemical properties. Here, we report a combined experimental and theoretical study on the variation of carrier-lattice interaction and optoelectronic properties of Cs2AgIn1-xBixCl6 double perovskite nanocrystals with varying alloying concentrations. Our UV-vis study confirms the parity allowed first direct transition for x ≤ 0.25. Using a careful analysis of Raman spectra assisted with first-principles simulations, we assign the possible three types of active modes to intrinsic atomic vibrations; 2 T2g modes (one for translational motion of "Cs" and other for octahedral breathing), 1 Eg and 1 A1g mode for various stretching of Ag-Cl octahedra. Ab-initio simulation reveals dominant carrier-phonon scattering via Fröhlich mechanism near room temperature, with longitudinal optical phonons being effectively activated around 230 K. We observe a noticeable increase in hole mobility (â¼4 times) with small Bi alloying, attributed to valence band (VB) maxima acquiring Bi-s orbital characteristics, thus resulting in a dispersive VB. We believe that our results should help to gain a better understanding of the intrinsic electronic and lattice dynamical properties of these compounds and provide a base toward improving the overall performance of double perovskite nanocrystals.
