Generalized Gradient Approximation Exchange-correlation Functionals Research Articles

High-throughput density functional theory screening of double transition metal MXene precursors

MXenes are an emerging class of 2D materials of interest in applications ranging from energy storage to electromagnetic shielding. MXenes are synthesized by selective etching of layered bulk MAX phases into sheets of 2D MXenes. Their chemical tunability has been significantly expanded with the successful synthesis of double transition metal MXenes. While knowledge of the structure and energetics of double transition metal MAX phases is critical to designing and optimizing new MXenes, only a small subset of these materials been explored. We present a comprehensive dataset of key properties of MAX phases obtained using density functional theory within the generalized gradient approximation exchange-correlation functionals. Energetics and structure of 8,712 MAX phases have been calculated and stored in a queryable, open database hosted at nanoHUB.

Temperature effects in static and dynamic polarizabilities from distinct generalized gradient approximation exchange-correlation functionals

To demonstrate that there are specific temperature effects in the description of static and dynamic polarizabilities which arise from generalized gradient approximation exchange-correlation functionals that obey distinctive asymptotic constraints, we present calculations for a test set of small molecules, at the experimental geometry, at the optimized ground-state geometry, and at the Born-Oppenheimer molecular dynamics geometries that arise from simulating a temperature of 300K. The results indicate that a functional with the correct asymptotic potential (CAP) provides a better description at room temperature than does a GGA functional with an exponentially decaying exchange potential such as PBE.

Properties of the silver cyclic amide Ag2(C4H4NO2)2(H2O) crystal from the periodic DFT computations

A molecular crystal of silver cyclic amide Ag2(C4H4NO2)2(H2O) is studied using first-principles density functional theory calculations within the generalized gradient approximation (GGA). A number of different exchange-correlation functionals are considered for a possible treatment of the system. It is found that the Perdew-Burke-Ernzerhof (PBE) GGA exchange-correlation functionals are adequate for the Ag2(C4H4NO2)2(H2O) crystal. The results obtained show the possibility to reproduce rather well the geometry of at least some molecular crystals by means of the periodic solid-state calculations if the computational parameters are chosen adequately. The present work also reports the analysis of the chemical bonding in the material and gives the total and partial density of states. Our solid-state computations point out the possible magnetic properties of the molecular crystal under study.

Density functional theory study of the relative stability of the iron disulfide polymorphs pyrite and marcasite

The performance of density functional theory has been widely examined with regard to its ability to predict the properties of minerals, though less attention has been given to the correct determination of the relative stability of structurally similar polymorphs. Here a detailed examination is performed of the numerical and theoretical factors that may influence the structure and relative energetics of two such polymorphs of iron disulfide, namely, pyrite and marcasite, within density functional theory. Both the local-density approximation and commonly used generalized gradient approximation exchange-correlation functionals, such as Perdew, Burke and Ernzerhof (PBE), are found to predict that marcasite is more stable than pyrite, at variance with experiment. Allowing for the zero-point energy of vibration fails to remedy this discrepancy. While inclusion of a sufficiently large Hubbard $U$ parameter for iron is found to reverse the stability, this comes at the expense of a very poor description of other properties. Examination of three generalized gradient approximations developed specifically for the solid state, namely, AM05, Wu-Cohen and PBEsol, demonstrates that all of these functionals offer a superior description of the structures and relative energies of pyrite and marcasite through correctly predicting that the former is the ground-state phase at ambient conditions.

Real-time propagation of the reduced one-electron density matrix in atom-centered Gaussian orbitals: Application to absorption spectra of silicon clusters

We solve the time-dependent density functional theory equation by propagating the reduced one-electron density matrix in real-time domain. The efficiency of several standard solvers such as the short-iterative Krylov-subspace propagator, the low-order Magnus integration method with the matrix polynomial (MP) or Chebyshev matrix polynomial (CMP) expansion of the evolution operator, and Runge-Kutta algorithm are assessed. Fast methods for summing MP and CMP are implemented to speed the calculation of the matrix exponential. It is found that the exponential propagators can tolerate large time step size and retain the computational accuracy whereas the Krylov-subspace algorithm is a little inferior for a larger time step size compared with the second-order Magnus integration method with the MP/CMP expansion of the evolution operator in both weak and intense fields. As an application, we calculate the absorption spectra of hydrogen-passivated silicon nanoparticles Si(29)H(x). The popular hybrid and generalized gradient approximation exchange-correlation functionals are applied. We find that the experimental spectra can be reproduced by using B3LYP and that the silicon particles with sizes of 1 nm and the optical excitations at 3.7, 4.0, and 4.6 eV may consist of 29 Si atoms surrounded by 24 hydrogen atoms.

Density functional generalized gradient calculations using Slater basis sets

The most common form of density functional calculations on molecular systems used generalized gradient approximation exchange-correlation functionals (such calculations can be applied to larger systems because no exact exchange is included). The most efficient and fastest such codes use an auxiliary basis set to fit the density so that only three-center integrals need to be evaluated. The codes DGAUSS and TURBOMOL use Gaussian basis sets, whereas the long-established ADF code uses Slater basis sets. We here examine the use of Slater basis sets. Our new code evaluates all required integrals numerically by quadrature. We report calculations on the G2 molecular set, contrasting them with similar calculations using Gaussian basis sets. Our conclusion, as far as energetics and structure are concerned, is that very similar predictions may be obtained from basis sets of the same size, and at approximately the same cost.

Molecular and dissociative chemisorption of NO on palladium and rhodium (100) and (111) surfaces: A density-functional periodic study

The efforts to reduce NOx pollutants have stimulated a large interest in the understanding of the elementary processes for NO transformation on transition metal surfaces. Periodic density-functional calculations have been performed for the molecular and dissociative chemisorption of NO on Pd and Rh(100) and (111) surfaces, with generalized gradient approximation exchange-correlation functionals. The periodic systems are modeled by two-dimensional palladium or rhodium slabs with frozen geometry, on which a NO, N, O, or (N+O) adlayer is set. On Pd and Rh(100) at a coverage of 0.5 monolayer (ML), the bridge site is the most stable one with respective binding energies of −1.54 and −2.18 eV. On the (111) surfaces, at a coverage of 0.33 ML, the threefold hollow sites are favored with binding energies of −2.0 eV for Pd(111) and −2.18 eV for Rh(111). For the dissociated structures, the mixed coadsorption of N and O is favored in most cases compared to separated domains. The chemisorption of NO, N, or O is stronger on Rh surfaces than on Pd ones but the stability gain is larger for the atomic chemisorption. The absolute values of binding energies decrease with the coverage. The NO dissociation is exothermic only for Rh at low coverage, while it is endothermic on Pd due to smaller atomic binding energies. This reaction becomes more endothermic when the coverage increases.