Meta GGA Research Articles

Revealing the remarkably improved structural, phonon, elastic, optoelectronic and thermoelectric properties of TlXF3(X [formula omitted] Ca, Cd) for energy applications using first-principles approach with hybrid and range-separated hybrid functionals

This study reports the first-principles investigations of flouroperovskites, TlXF3(X = Ca, Cd), within the frame work of Density Functional Theory. A comprehensive and improved data of flouroperovskites on structural, phonon, elasto-mechanical, optoelectronic and thermoelectric properties are carried out using Perdew Burke Ernzerhof-Generalized Gradient Approximation (PBE-GGA), Trans-Blaha modified Becke–Johnson (TB-mBJ), meta GGA, Strongly Constrained and Appropriately Normed (SCAN), hybrid functional including Becke’s three parameter exchange functional with the Lee–Yang–Parr (B3LYP) and range-separated hybrid functional Heyd–Scuseria–Ernzerhof (HSE06). The structures are optimized and stability is proved by energy-volume optimization, formation energy calculations, positive phonon frequencies of phonon dispersion curves and elastic constant criteria. The electronic band structures of both TlCaF3 and TlCdF3 possess direct and indirect nature respectively and density of states are consistent with electronic band structure. The band gaps of TlCaF3 are 4.53 eV (PBE-GGA), 6.19 eV (TB-mBJ), 4.89 eV (SCAN), 6.24 eV (B3LYP) and 5.98 eV (HSE06) and the band gaps of TlCdF3 are 3.74 eV (PBE-GGA), 5.64 eV (TB-mBJ), 4.30 eV (SCAN), 5.83 eV (B3LYP) and 5.53 eV (HSE06). The dynamical stability and brittle response of TlCaF3 and TlCdF3 is confirmed from shear constant, Pugh’s ratio and Poisson’s ratio. The optical and thermoelectric response are studied for optoelectronic and sustainable applications.

First-Principles insights to probe structural and opto-electronic properties of [formula omitted] (Y=Mg, Sr) halide perovskites with variety of DFT methods

This study reports the structural, electronic, optical, phonon, thermodynamic and thermoelectric properties of AgYF3 (X=Mg, Sr) for photovoltaic and energy applications. We performed first principles calculations using full potential linearized augmented plane wave, FP-LAPW method implemented in Wien2k. The generalized gradient approximations of Perdew–Burke–Ernzerhof PBE-GGA, and PBE revised for solids, PBEsol, is employed for structural optimization of these lead free halide perovskites. The Birch–Murnaghan energy volume curve fitting comprehend the structural stability. The optimized lattice constant of AgMgF3 and AgSrF3 obtained with PBE-GGA(PBEsol) is 3.99(3.92)Å and 4.42(4.65)Å. The stability is further tested with the help of formation energy and positive phonon dispersion curves calculations. For the calculations of explicit electronic and optical properties, we also employed Tran–Blaha modified Beck–Johnson (TB-mBJ) and Strongly Constrained but Appropriately Normed, SCAN, exchange and correlations functionals. The electronic band gap of AgMgF3 computed with PBEsol, TB-mBJ and SCAN is 1.96 eV, 5.25 eV and 2.59 eV exhibiting M-Γ indirect band gap. The band gap energy of AgSrF3 is 2.06 eV, 6.42 eV and 2.70 eV with PBEsol, TB-mBJ and SCAN. The indirect band gap nature of AgSrF3 is confirmed by PBEsol and TB-mBJ while it anticipated direct band gap behavior with meta-GGA SCAN. The different optical parameters like dielectric constant, optical conductivity, energy loss function, absorption, reflectivity and refractive index are calculated to assess optical activity of both perovskites. Comprehensive electronic and optical analysis advocates the utility of AgMgF3 and AgSrF3 for different applications is solar technology and optoelectronic devices.

A reactive neural network framework for water-loaded acidic zeolites

Under operating conditions, the dynamics of water and ions confined within protonic aluminosilicate zeolite micropores are responsible for many of their properties, including hydrothermal stability, acidity and catalytic activity. However, due to high computational cost, operando studies of acidic zeolites are currently rare and limited to specific cases and simplified models. In this work, we have developed a reactive neural network potential (NNP) attempting to cover the entire class of acidic zeolites, including the full range of experimentally relevant water concentrations and Si/Al ratios. This NNP has the potential to dramatically improve sampling, retaining the (meta)GGA DFT level accuracy, with the capacity for discovery of new chemistry, such as collective defect formation mechanisms at the zeolite surface. Furthermore, we exemplify how the NNP can be used as a basis for further extensions/improvements which include data-efficient adoption of higher-level (hybrid) references via Δ-learning and the acceleration of rare event sampling via automatic construction of collective variables. These developments represent a significant step towards accurate simulations of realistic catalysts under operando conditions.

Beyond Explored Functionals: A Computational Journey of Two-Photon Absorption.

We present a thorough investigation into the efficacy of 19 density functional theory (DFT) functionals, relative to RI-CC2 results, for computing two-photon absorption (2PA) cross sections (σ2PA) and key dipole moments (|μ00|, |μ11|, |Δμ|, |μ01|) for a series of coumarin dyes in the gas-phase. The functionals include different categories, including local density approximation (LDA), generalized gradient approximation (GGA), hybrid-GGA (H-GGA), range-separated hybrid-GGA (RSH-GGA), meta-GGA (M-GGA), and hybrid M-GGA (HM-GGA), with 14 of them being subjected to analysis for the first time with respect to predicting σ2PA values. Analysis reveals that functionals integrating both short-range (SR) and long-range (LR) corrections, particularly those within the RSH-GGA and HM-GGA classes, outperform the others. Furthermore, the range-separation approach was found more impactful compared to the varying percentages of Hartree-Fock exchange (HF Ex) within different functionals. The functionals traditionally recommended for 2PA do not appear among the top 9 in our study, which is particularly interesting, as these top-performing functionals have not been previously investigated in this context. This list is dominated by M11, QTP variants, ωB97X, ωB97X-V, and M06-2X, surpassing the performance of other functionals, including the commonly used CAM-B3LYP.

Theoretical DFT Investigation of Structure and Electronic Properties of η5-Cyclopentadienyl Half-Sandwich Organochalcogenide Complexes

For the first time, an extensive theoretical comparative study of the electronic structure and spectra of the η5-cyclopentadienyl half-sandwich [(Cp)(EPh3)], E = Se, Te) organochalcogenides was carried out using direct space electronic structure calculations within hybrid, meta, and meta-hybrid DFT GGA functionals coupled with double-ζ polarized 6-31G* and correlation-consistent triple-zeta cc-pVTZ-pp basis sets. The absence of covalent bonding between the cyclopentadienyl (Cp) ligands and Te/Se coordination centers was revealed. It was found that the chalcogens are partially positively charged and Cp ligands are partially negatively charged, which directly indicates a visible ionic contribution to Te/Se-Cp chemical bonding. Simulated UV–Vis absorption spectra show that all complexes have a UV-active nature, with a considerable shift in their visible light absorption due to the addition of methyl groups. The highest occupied molecular orbitals exhibit π-bonding between the Te/Se centers and Cp rings, although the majority of the orbital density is localized inside the Cp π-system. The presence of the chalcogen atoms and the extension of π-bonds across the chalcogen-ligand interface make the species promising for advanced photovoltaic and light-emitting applications.

Revealing the ground‐state geometry, optoelectronic, mechanical and thermodynamic behaviors, and efficiency of formamidinium mixed halide perovskites for solar cell applications

Hybrid organic-inorganic lead halide perovskites are the revolutionary materials that have brought a new era of low-cost and highly efficient solar cells. Generally, high-performing perovskite solar cells incorporate formamidinium-based lead halide perovskites. Using density functional theory, we employed generalized gradient approximation (GGA) and meta-GGA (MGGA) exchange-correlation functionals to investigate the structural, electronic, optical, mechanical, and thermodynamic properties of the perovskite series FAPbI3, FAPbBr2I, FAPbBrI2, and FAPbBr3. Both the functionals successfully determined the most stable structure for each mixed halide perovskite. Electronic properties such as band structure, the density of states, and effective masses have been calculated and discussed. Our estimated band gap values using MGGA functional are more close to the experiments than PBE. Optical properties of the perovskite series such as dielectric function, complex refractive index, absorption coefficient, and reflectivity have been explained in the light of photovoltaic applications. Moreover, we predicted the maximum absorber efficiency via the spectroscopic limited maximum efficiency method. FAPbI3 achieved the highest efficiency by virtue of its suitable band gap and maximum absorption. Mechanical properties have also been studied through elastic constants, elastic moduli, Pugh ratio, Poisson ratio, and other several properties, which reveal the declining flexibility of perovskites with bromine. Further, thermodynamic properties like heat capacity, Debye temperature, vibrational internal energy, vibrational entropy, thermal expansion, and thermal stability have been discussed and analyzed. Among all perovskites, the thermodynamic stability of FAPbBr2I is found superior due to strong Br-I bonds and the tougher attraction of the ionic system in the perovskite lattice. All the results are compared with earlier reported values and found to be in fair agreement.

O2 on Ag(110): A puzzle for exchange-correlation functionals

Despite the great success of density functional theory in describing materials, there are still a few examples where current exchange-correlation functionals fail. We add another example to this list that drives further development of functionals. We show that the interaction of O$_2$ with Ag(110) cannot be properly described by some of the most popular GGA, meta GGA, and hybrid functionals. We identify problems and provide clues for a functional that should be able to describe this and similar systems properly.

EQE 2.0: Subsystem DFT beyond GGA functionals

By adopting a divide-and-conquer strategy, subsystem-DFT (sDFT) can dramatically reduce the computational cost of large-scale electronic structure calculations. The key ingredients of sDFT are the nonadditive kinetic energy and exchange-correlation functionals which dominate it's accuracy. Even though, available semilocal nonadditive functionals find a broad range of applications, their accuracy is somewhat limited especially for those systems where achieving balance between exchange-correlation interactions on one side and nonadditive kinetic energy on the other is crucial. In eQE 2.0, we improve dramatically the accuracy of sDFT simulations by (1) implementing nonlocal nonadditive kinetic energy functionals based on the LMGP family of functionals; (2) adapting Quantum ESPRESSO's implementation of rVV10 and vdW-DF nonlocal exchange-correlation functionals to be employed in sDFT simulations; (3) implementing “deorbitalized” meta GGA functionals (e.g., SCAN-L). We carefully assess the performance of the newly implemented tools on the S22-5 test set. eQE 2.0 delivers excellent interaction energies compared to conventional Kohn-Sham DFT and CCSD(T). The improved performance does not come at a loss of computational efficiency. We show that eQE 2.0 with nonlocal nonadditive functionals retains the same linear scaling behavior achieved previously in eQE 1.0 with semilocal nonadditive functionals. Program summaryProgram title: eQECPC Library link to program files:https://doi.org/10.17632/g55n9xmnt2.1Developer's repository link:https://gitlab.com/Pavanello/eqeLicensing provisions: GPLv2Programming language: Fortran 90External routines/libraries: BLACS, MPINature of problem: Solving the electronic structure of molecules and materials with subsystem density functional theorySolution method: This version of eQE uses subsystem Density-Functional Theory (DFT) to compute the electronic structure of molecules and materials. Subsystem DFT is a divide-and-conquer version of DFT that can be massively parallelized and is linear scaling in work and data. However, it requires the use of density functionals for kinetic and exchange-correlation energies. eQE can now employ nonlocal functionals as well as meta-GGA functionals for these energy terms.Additional comments: Url of stable release http://eqe.rutgers.edu

Theoretical insight on antioxidant potency of kanzakiflavone-2 and its derivatives

Functional groups in flavonoids always act as deciding factors in making a particular flavonoid to be active. They possess the capability to enhance or diminish the structural activity of flavonoids. The idea about conjugated functional units and their role over structural activity alteration still seems to be less explored. In the present work, kanzakiflavone and its derivatives possessing the structural activity directors –OH, -OCH3, and –O-CH2-O- are analyzed using density functional theory with help of global hybrid meta GGA correlation functional (M06-2X) under the basis set 6-311++G(d,p). Energy surface analysis (frontier molecular orbitals and electrostatic potential) based on charge distribution shows that the studied flavonoids prefer to act as potential electron donors. Interestingly, the electron rich area (A-ring) is profound to be altered with B-ring in comparison with other flavones. All the studied flavonoids prefer to act as potential radical scavengers in aqueous phase which is witnessed via antioxidant mechanisms. Absorption, digestion, metabolism, and excretion (ADME) analysis was carried out to understand the nominal role of flavonoids to meet medicinal applications. Kanzakiflavone and its derivatives prefer to act as possible leads based on physiological, pharmacological, and lipophilic properties.

Density Functional Theory Meta GGA Study of Water Adsorption in MIL-53(Cr).

We use density functional theory meta-GGA TPSS+D3(BJ)+U+J calculations to investigate the energetics and geometry of water molecules in the flexible metal-organic framework material MIL-53(Cr) as a function of cell volume. The critical concentration of water to cause the transition from the large pore (lp) to the narrow pore (np) structure is estimated to be about 0.13 water molecule per Cr. At a concentration x = 1 water molecule per Cr, the zero-temperature np and lp configurations each have a hydrogen bond between the H of each framework hydroxyl group and a water oxygen (O W ). At intermediate volumes, water dimer-like configurations are observed. A concentration x = 1.25 leads to hydrogen bonding between water molecules in the np phase that is absent for x = 1. Our results suggest possible mechanisms for pore closing in hydrated MIL-53(Cr).

First-principles study of mechanical and electronic properties of bent monolayer transition metal dichalcogenides

The mechanical and electronic properties of transition metal dichalcogenide (TMD) monolayers corresponding to transition groups IV, VI, and X are explored under mechanical bending from first principles calculations using the strongly constrained and appropriately normed (SCAN) meta-GGA (MGGA). SCAN provides an accurate description of the phase stability of the TMD monolayers. Our calculated lattice parameters and other structural parameters agree well with experiment. We find that bending stiffness (or flexural rigidity) increases as the transition metal group goes from IV to X to VI, with the exception of PdTe$_2$. Variation in mechanical properties (local strain, physical thickness) and electronic properties (local charge density, band structure) with bending curvature is discussed. The local strain profile of these TMD monolayers under mechanical bending is highly non-uniform. The mechanical bending tunes not only the thickness of the TMD monolayers but also the local charge distribution as well as the band structures, adding more functionalization options to these materials.

Assessment of DFT for endohedral complexes' dipole moment: PNO-LCCSD-F12 as a reference method.

We present a systematic evaluation of the performance of a wide range of exchange-correlation functionals and related dispersion correction schemes for the computation of dipole moments of endohedral complexes, formed through the encapsulation of an AB molecule (AB = LiF, HCl) inside carbon nanotubes (CNTs) of different diameter. The consistency and accuracy of (i) generalized gradient approximation, (ii) meta GGA, (iii) global hybrid, and (iv) range-separated hybrid density functionals are assessed. In total, 37 density functionals are tested. The results obtained using the highly accurate pair natural orbitals based explicitly correlated local coupled cluster singles doubles (PNO-LCCSD-F12) method of Werner and co-workers [Schwilk et al., J. Chem. Theory Comput., 2017, 13, 3650; Ma et al., J. Chem. Theory Comput., 2017, 13, 4871] with the aug-cc-pVTZ basis set serve as a reference. The static electric dipole moment is computed via the finite field response or, when possible, as the expectation value of the dipole operator. Among others, it is shown that functionals belonging to the class of range-separated hybrids, provide results closest to the coupled cluster reference data. In particular, the ωB97X as well as the M11 functional may be considered as a promising choice for computing electric properties of noncovalent endohedral complexes. On the other hand, the worst performance was found for the functionals which do not include the Hartree-Fock exchange. The analysis of both the coupled cluster and the DFT results indicates a strong coupling of dispersion and polarization that may also explain why lower level DFT methods, as well as Hartree-Fock and MP2, cannot yield dipole moments beyond a qualitative agreement with the higher order reference data. Interestingly, the much smaller and less systematically constructed basis sets of Pople of moderate size provide results of accuracy at least comparable with the extended Dunning's aug-cc-pVTZ basis set.

Exchange functionals based on finite uniform electron gases.

We show how one can construct a simple exchange functional by extending the well-know local-density approximation (LDA) to finite uniform electron gases. This new generalized local-density approximation functional uses only two quantities: the electron density ρ and the curvature of the Fermi hole α. This alternative "rung 2" functional can be easily coupled with generalized-gradient approximation (GGA) functionals to form a new family of "rung 3" meta-GGA (MGGA) functionals that we have named factorizable MGGAs. Comparisons are made with various LDA, GGA, and MGGA functionals for atoms and molecules.

A simple model for the Slater exchange potential and its performance for solids

AbstractA simple local model for the Slater exchange potential is determined by least square fit procedure from Hartree–Fock (HF) atomic data. Since the Slater potential is the exact exchange potential yielding HF electron density from Levy‐Perdew‐Sahni density functional formalism (Levy et al., Phys. Rev. A 1984, 30, 2745), the derived local potential is significantly more negative than the conventional local density approximation. On the set of 22 ionic, covalent and van der Waals solids including strongly correlated transition metal oxides, it has been demonstrated, that this simple model potential is capable of reproducing the band gaps nearly as good as popular meta GGA potentials in close agreement with experimental values.

Comparative assessment of density functional methods for evaluating essential parameters to simulate SERS spectra within the excited state energy gradient approximation

The prospect of challenges in reproducing and interpretation of resonance Raman properties of molecules interacting with metal clusters has prompted the present research initiative. Resonance Raman spectra based on the time-dependent gradient approximation are examined in the framework of density functional theory using different methods for representing the exchange-correlation functional. In this work the performance of different XC functionals in the prediction of ground state properties, excitation state energies, and gradients are compared and discussed. Resonance Raman properties based on time-dependent gradient approximation for the strongly low-lying charge transfer states are calculated and compared for different methods. We draw the following conclusions: (1) for calculating the binding energy and ground state geometry, dispersion-corrected functionals give the best performance in comparison to ab initio calculations, (2) GGA and meta GGA functionals give good accuracy in calculating vibrational frequencies, (3) excited state energies determined by hybrid and range-separated hybrid functionals are in good agreement with EOM-CCSD calculations, and (4) in calculating resonance Raman properties GGA functionals give good and reasonable performance in comparison to the experiment; however, calculating the excited state gradient by using the hybrid functional on the hessian of GGA improves the results of the hybrid functional significantly. Finally, we conclude that the agreement of charge-transfer surface enhanced resonance Raman spectra with experiment is improved significantly by using the excited state gradient approximation.

Interaction of Ruthenium(II) with Terminal Alkynes: Benchmarking DFT Methods with Spectroscopic Data

Helium tagging infrared photodissociation (IRPD) spectroscopy for the characterization of organometallic complexes is presented. The IRPD spectrum of the [RuCp(PPh3)(PhCCH)]+ complex reveals that more than 80% of the detected ions correspond to a structure with π-coordinated phenylacetylene, and the rest are complexes with the alkyne probably isomerized to its vinylidene form. The detected C≡C and C–H stretches of the terminal alkyne reflect the degree of activation of the triple bond. They are used to benchmark the popular DFT functionals used in theoretical studies of ruthenium catalysis. It is shown that there are only small differences between the methods. GGA methods (e.g., BP86 or PBEPBE) and (hybrid) meta GGA functionals (e.g., M06) provide slightly better descriptions of this system than hybrid DFT methods such as B3LYP. A notable exception is M06-2X, which significantly underestimates the activation of the C≡C bond by the coordination to the ruthenium complex.

The effects of uniaxial and biaxial strain on the electronic structure of germanium

The effects of uniaxial and biaxial strain on the electronic structure of bulk germanium are investigated using density functional theory in conjunction with four approximations for the exchange correlation interaction: the local density approximation (LDA) and generalized gradient approximation (GGA) with on-site Hubbard corrections (LDA+U, GGA+U), the meta-GGA (MGGA), and the screened hybrid functional (HSE06). The band structure and, especially, the band gap of unstrained Ge are well reproduced by these methods. The results of LDA+U/GGA+U and MGGA show that a biaxial tensile strain above 1.5% turns Ge into a direct-gap (Γ–Γ) semiconductor, whereas the indirect Γ–L gap is maintained for uniaxial strain up to 3%. The HSE06 results confirm a similar trend, although the predicted critical strain is lower. The effective masses were also calculated and they were found to be in good agreement with experiments for bulk Ge. It is predicted that the masses at Γ can be tuned to be smaller/larger by tensile/compressive strain in all directions.

Density functionals that recognize covalent, metallic, and weak bonds.

Computationally efficient semilocal approximations of density functional theory at the level of the local spin density approximation (LSDA) or generalized gradient approximation (GGA) poorly describe weak interactions. We show improved descriptions for weak bonds (without loss of accuracy for strong ones) from a newly developed semilocal meta-GGA (MGGA), by applying it to molecules, surfaces, and solids. We argue that this improvement comes from using the right MGGA dimensionless ingredient to recognize all types of orbital overlap.

Nonlocal van der Waals Approach Merged with Double-Hybrid Density Functionals: Toward the Accurate Treatment of Noncovalent Interactions.

Noncovalent interactions drive the self-assembly of weakly interacting molecular systems to form supramolecular aggregates, which play a major role in nanotechnology and biochemistry. In this work, we present a thorough assessment of the performance of different double-hybrid density functionals (PBE0-DH-NL, revPBE0-DH-NL, B2PLYP-NL, and TPSS0-DH-NL), as well as their parent hybrid and (meta)GGA functionals, in combination with the most modern version of the nonlocal (NL) van der Waals correction. It is shown that this nonlocal correction can be successfully coupled with double-hybrid density functionals thanks to the short-range attenuation parameter b, which has been optimized against reference interaction energies of benchmarking molecular complexes (S22 and S66 databases). Among all the double-hybrid functionals evaluated, revPBE0-DH-NL and B2PLYP-NL behave remarkably accurate with mean unsigned errors (MUE) as small as 0.20 kcal/mol for the training sets and in the 0.25-0.42 kcal/mol range for an independent database (NCCE31). They can be thus seen as appropriate functionals to use in a broad number of applications where noncovalent interactions play an important role. Overall, the nonlocal van der Waals approach combined with last-generation density functionals is confirmed as an accurate and affordable computational tool for the modeling of weakly bonded molecular systems.

Experimental and quantum chemical studies of a novel synthetic prenylated chalcone

BackgroundChalcones are ubiquitous natural compounds with a wide variety of reported biological activities, including antitumoral, antiviral and antimicrobial effects. Furthermore, chalcones are being studied for its potential use in organic electroluminescent devices; therefore the description of their spectroscopic properties is important to elucidate the structure of these molecules. One of the main techniques available for structure elucidation is the use of Nuclear Magnetic Resonance Spectroscopy (NMR). Accordingly, the prediction of the NMR spectra in this kind of molecules is necessary to gather information about the influence of substituents on their spectra.ResultsA novel substituted chalcone has been synthetized. In order to identify the functional groups present in the new synthesized compound and confirm its chemical structure, experimental and theoretical 1H-NMR and 13C-NMR spectra were analyzed. The theoretical molecular structure and NMR spectra were calculated at both the Hartree-Fock and Density Functional (meta: TPSS; hybrid: B3LYP and PBE1PBE; hybrid meta GGA: M05-2X and M06-2X) levels of theory in combination with a 6-311++G(d,p) basis set. The structural parameters showed that the best method for geometry optimization was DFT:M06-2X/6-311++G(d,p), whereas the calculated bond angles and bond distances match experimental values of similar chalcone derivatives. The NMR calculations were carried out using the Gauge-Independent Atomic Orbital (GIAO) formalism in a DFT:M06-2X/6-311++G(d,p) optimized geometry.ConclusionConsidering all HF and DFT methods with GIAO calculations, TPSS and PBE1PBE were the most accurate methods used for calculation of 1H-NMR and 13C-NMR chemical shifts, which was almost similar to the B3LYP functional, followed in order by HF, M05-2X and M06-2X methods. All calculations were done using the Gaussian 09 software package. Theoretical calculations can be used to predict and confirm the structure of substituted chalcones with good correlation with the experimental data.