Modern Density Functional Theory Research Articles

Theoretical Photoelectron Spectroscopy of Quadruple-Bonded Dimolybdenum(II,II) and Ditungsten(II,II) Paddlewheel Complexes: Performance of Common Density Functional Theory Methods.

We have revisited the gas-phase photoelectron spectra of quadruple-bonded dimolybdenum(II,II) and ditungsten(II,II) paddlewheel complexes with modern density functional theory methods and obtained valuable calibration of four well-known exchange-correlation functionals, namely, BP86, OLYP, B3LYP*, and B3LYP. All four functionals were found to perform comparably, with discrepancies between calculated and experimental ionization potentials ranging from <0.1 to ∼0.5 eV, with the lowest errors observed for the classic pure functional BP86. All four functionals were found to reproduce differences in ionization potentials (IPs) between analogous Mo2 and W2 complexes, as well as large, experimentally observed ligand field effects on the IPs, with near-quantitative accuracy. The calculations help us interpret a number of differences between analogous Mo2 and W2 complexes through the lens of relativistic effects. Thus, relativity results in not only significantly lower IPs for the W2 complexes but also smaller HOMO-LUMO gaps and different triplet states relative to their Mo2 counterparts.

Temperature-induced suppression of structural disproportionation in paramagnetic quantum materials

With the development of electronic structure theory, a new class of materials—quantum ones—has been recognized by the community. Traditionally, it has been believed that the properties of such compounds cannot be described within the framework of modern density functional theory, and indeed, more advanced post-mean-field theory methods are needed. Motivated by this, herein, we develop a fundamental understanding of such complex materials using the example of paramagnetic YNiO3, which is experimentally known to exhibit metal-to-insulator phase transition. We show that this material has a temperature-dependent distribution of local motifs. Thus, while at low temperatures, YNiO3 has distinct structural disproportionation with the formation of large and small octahedra, as the temperature increases, this disproportionation is suppressed. We also explain the paramagnetic monoclinic to paramagnetic orthorhombic phase transition within the double-well to single-well energy profile, predicting the variation in the corresponding energy profile as a function of octahedral size distribution. In this way, we demonstrate a fundamental understanding of structural phase transitions in quantum materials, giving insights into how they can be used for different applications and what minimum level of theory is needed to describe such types of complex materials at finite temperatures.

Density functional theory investigations on the mechanisms of homogeneous Sm complex catalyzed CO[formula omitted] cycloaddition with epoxides

Converting excess CO2 into chemically valuable products is a promising routine for sustainable development. Catalyzing epoxides and CO2 cycloaddition reactions homogeneously with rare-earth compounds is an emerging approach. The reaction efficiency can be understood by mechanism study. In this work, we report a detailed density functional theory investigation on a well-designed experimental Sm catalyst. We calibrate the ωB97XD exchange–correlation functional as the best candidate functional for this specific catalytic system. The energetic span of catalytic cycle is approximately 25 kcal mol−1. The rate-determining transition state is the one for ring-closure to generate the product. Two competing paths are revealed. Through both ionic and covalent metal–ligand interactions, the lowering of the epoxide substrate ring-opening step barrier is significant compared with the Sm compound free case. This work demonstrate the values for utilizing modern density functional theory to complement the understandings on the homogeneous rare-earth catalytic processes.

Extension of the D3 and D4 London dispersion corrections to the full actinides series.

Efficient dispersion corrections are an indispensable component of modern density functional theory, semi-empirical quantum mechanical, and even force field methods. In this work, we extend the well established D3 and D4 London dispersion corrections to the full actinides series, francium, and radium. To keep consistency with the existing versions, the original parameterization strategy of the D4 model was only slightly modified. This includes improved reference Hirshfeld atomic partial charges at the ωB97M-V/ma-def-TZVP level to fit the required electronegativity equilibration charge (EEQ) model. In this context, we developed a new actinide data set called AcQM, which covers the most common molecular actinide compound space. Furthermore, the efficient calculation of dynamic polarizabilities that are needed to construct CAB6 dispersion coefficients was implemented into the ORCA program package. The extended models are assessed for the computation of dissociation curves of actinide atoms and ions, geometry optimizations of crystal structure cutouts, gas-phase structures of small uranium compounds, and an example extracted from a small actinide complex protein assembly. We found that the novel parameterizations perform on par with the computationally more demanding density-dependent VV10 dispersion correction. With the presented extension, the excellent cost-accuracy ratio of the D3 and D4 models can now be utilized in various fields of computational actinide chemistry and, e.g., in efficient composite DFT methods such as r2SCAN-3c. They are implemented in our freely available standalone codes (dftd4, s-dftd3) and the D4 version will be also available in the upcoming ORCA 6.0 program package.

A Quantum-Chemical Bonding Database for Solid-State Materials

An in-depth insight into the chemistry and nature of the individual chemical bonds is essential for understanding materials. Bonding analysis is thus expected to provide important features for large-scale data analysis and machine learning of material properties. Such chemical bonding information can be computed using the LOBSTER software package, which post-processes modern density functional theory data by projecting the plane wave-based wave functions onto an atomic orbital basis. With the help of a fully automatic workflow, the VASP and LOBSTER software packages are used to generate the data. We then perform bonding analyses on 1520 compounds (insulators and semiconductors) and provide the results as a database. The projected densities of states and bonding indicators are benchmarked on standard density-functional theory computations and available heuristics, respectively. Lastly, we illustrate the predictive power of bonding descriptors by constructing a machine learning model for phononic properties, which shows an increase in prediction accuracies by 27% (mean absolute errors) compared to a benchmark model differing only by not relying on any quantum-chemical bonding features.

Self-consistent and detailed opacities from a non-equilibrium average-atom model.

Modern density functional theory (DFT) is a powerful tool for accurately predicting self-consistent material properties such as equations of state, transport coefficients and opacities in high energy density plasmas, but it is generally restricted to conditions of local thermodynamic equilibrium (LTE) and produces only averaged electronic states instead of detailed configurations. We propose a simple modification to the bound-state occupation factor of a DFT-based average-atom model that captures essential non-LTE effects in plasmas-including autoionization and dielectronic recombination-thus extending DFT-based models to new regimes. We then expand the self-consistent electronic orbitals of the non-LTE DFT-AA model to generate multi-configuration electronic structure and detailed opacity spectra. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.

Host–Guest Inclusion Systems of Vanillic Acid into α-Cyclodextrin: Structures, Electronic Properties, QTAIM, NCI and IGM Analyses with Dispersion Corrected Calculations

In this work, a theoretical study of the host–guest inclusion process involving the vanillic acid (VA) into α-cyclodextrin (α-CD) was investigated by the semi empirical methods PM6 and its modern variant PM6-D3H4 and density functional theory with the BP86-D3/6-31G+(d,p) functional to elucidate the relationship between host, guest and their molecular structures. According to the results from theoretical calculation, the model in which the VA molecule points it’s the carboxylic acid group toward the wider rim of α–CD is energetically preferred. The global reactivity descriptors were calculated and analyzed. The electronic transitions of the two complexes computed with the TD-DFT approach on the optimized geometries at BP86-D3/6-31G+ (d, p) level of theory including the CPCM model were investigated. Finally, quantum theory of atoms in molecules (QTAIM) analysis, the non-covalent interactions analysis (NCI) and the independent gradient model (IGM) results confirms that the van der Waals interactions and hydrogen bonds play a major role in the stabilization of the complexes.

Pseudopotential contributions to the quadrupole moment in charged periodic systems

There has been much interest over many years in studying charged systems after the artificial imposition of periodic boundary conditions, and correcting for the resulting divergence of the electrostatic energy density. A correction for cubic cells was derived by Makov and Payne in 1995, and its leading error term is of the form $L^{-5}$ for a cube of side $L$. Most modern Density Functional Theory codes use a different treatment of the `Z$\alpha$' energy term to that used by Makov and Payne, resulting in an error term of the form $L^{-3}$ if their correction is used unmodified. This paper shows how the Makov and Payne result can be made consistent with modern practice.

Interaction energy of Cl2 and Br2 with H2 O: Exchange, dispersion and density the crucial ingredients.

Modern Density Functional Theory models are now suitable for many molecular and condensed phase studies. The study of noncovalent interactions, a well-known drawback, is no longer an insurmountable obstacle through design and empirical corrections. However, using empirical corrections as in the DFT-D methods might not be an all-in-one solution. This work uses a simple system, X2 -H2 O with X=Cl or Br, with two different interactions, halogen-bonded (XB) and hydrogen-halogen (HX), to investigate the capability of current density functional approximations (DFA) in predicting interaction energies with eight different exchange-correlation functionals. SAPT(DFT) provides, for all the studied cases, better predictions than the widely used supermolecular approach. In addition, the components of the interaction energy suggest where some of the shortcomings originate in each DFA. The analysis of the functionals used confirms that PBE0 and ω-B97X-D have a physically correct behavior. Using SAPT(DFT) and PBE0, and ω-B97X-D, we obtained the interaction energy of Cl2 and Br2 inside different clathrate cages and satisfactorily compared with wavefunction results; hence, the lower and upper limits of this value are defined: Cl2 @512 , -5.3 ± 0.3kcal/mol; Cl2 @512 62 , -5.5 ± 0.1kcal/mol; Br2 @512 62 , -7.6 ± 1.0kcal/mol; Br2 @512 63 , -10.6 ± 1.0kcal/mol; Br2 @512 64 , -10.9 ± 0.8kcal/mol.

Rényi Entropies of Multidimensional Oscillator and Hydrogenic Systems with Applications to Highly Excited Rydberg States.

The various facets of the internal disorder of quantum systems can be described by means of the Rényi entropies of their single-particle probability density according to modern density functional theory and quantum information techniques. In this work, we first show the lower and upper bounds for the Rényi entropies of general and central-potential quantum systems, as well as the associated entropic uncertainty relations. Then, the Rényi entropies of multidimensional oscillator and hydrogenic-like systems are reviewed and explicitly determined for all bound stationary position and momentum states from first principles (i.e., in terms of the potential strength, the space dimensionality and the states's hyperquantum numbers). This is possible because the associated wavefunctions can be expressed by means of hypergeometric orthogonal polynomials. Emphasis is placed on the most extreme, non-trivial cases corresponding to the highly excited Rydberg states, where the Rényi entropies can be amazingly obtained in a simple, compact, and transparent form. Powerful asymptotic approaches of approximation theory have been used when the polynomial's degree or the weight-function parameter(s) of the Hermite, Laguerre, and Gegenbauer polynomials have large values. At present, these special states are being shown of increasing potential interest in quantum information and the associated quantum technologies, such as e.g., quantum key distribution, quantum computation, and quantum metrology.

The powder X-band electron paramagnetic resonance spectroscopy of septet pyridyl-2,4,6-trinitrene.

The first X-band EPR spectrum containing only non-overlapping signals of septet pyridyl-2,4,6-trinitrene and triplet pyridylnitrenes is reported. This spectrum was recorded after photolysis of 2,4,6-triazidopyridine in solid argon at 5 K. The zero-field splitting (ZFS) parameters of this trinitrene as well as of intermediate triplet mononitrenes and quintet dinitrenes formed at early stages of the photolysis were determined using the combination of modern computer line-shape spectral simulations and density functional theory (DFT) calculations. It was found that septet pyridyl-2,4,6-trinitrene has the record negative parameter DS = -0.1031 cm-1 among all known to date septet pyridyl-2,4,6-trinitrenes and may be of interest as a model multi-qubit spin system for investigations of quantum computation processing.

Construction of MoS2/graphite/C3N4 Ternary Photocatalytic System Through Communicating Electron

A MoS2/graphite/C3N4 ternary photocatalytic material (MGC catalyst) was successfully synthesized, characterized, and applied to the photodegradation of Methylene Blue (MB). In addition, the photocatalytic mechanism of MGC was illustrated through modern characterization technology and density functional theory (DFT) computation. The findings of characterization (XRD, SEM-EDX, UV-Vis, XPS) confirmed that MGC was a composite photocatalyst of C3N4-graphite-MoS2 ternary structure, and displayed excellent visible light absorption performance. MGC photocatalyst exhibited the highest degradation efficiencies of MB than that of C3N4 and MoS2 catalyst, and it effectively improved the removal of pollutant. Also, the first-order reaction model suitably described the photocatalytic reaction process. The recycling experiments proved that MGC catalyst possessed remarkable photocatalytic stability in the degradation activities of MB, and the morphology maintained stable after three times of reusing. The ternary composite structure of MGC was conducive to the generation and transfer of the photo-generated electrons and photo-generated holes. Besides, MGC photocatalyst obtained the lowest photoluminescence spectrum intensity, which might decrease the combination probability of photo-induced electrons and holes. Electron spin resonance (ESR) analysis verified that the active radicals of •OH and •O2- measured in photocatalytic reaction probably played an essential part in the degradation of MB. Furthermore, through calculating the band structure, density of states (DOS), and work function, it was illustrated that the two opposite potential barriers forming between graphite, MoS2 and C3N interface effectively accelerated the division of photo-induced electrons and photo-induced holes in MoS2 and C3N4. Then, the recombination probability of photo-induced electrons and holes was reduced, and hence that greatly improved the photocatalytic efficiency of MB.

Reactivity of short radicals at the initial stages of radical polymerization of allyl chloride: Chain growth versus addition to fullerene

AbstractA quantum‐chemical study of the C60 interaction with various radicals generated from monomers in radical polymerization is significant in the fundamental aspects. However, the interactions between fullerene and radicals formed from allyl monomers has been poorly studied. Using the modern density functional theory methods, we performed quantum‐chemical simulation on the C60 interaction with the radicals arising upon the initial stages of the allyl chloride polymerization. We have found that the addition of growth radicals (with 1–4 monomer units) to C60 are more favorable than the chain growth reactions. Herewith, the radicals with 2–4 monomer units are most reactive in the addition reaction. Our quantum‐chemical findings explain the features of the initial stages of the allyl chloride radical polymerization in the presence of C60, namely, the increasing inhibition degree of the radical copolymerization of allyl chloride with methyl methacrylate and increasing induction period of copolymerization with styrene.

OrbNet Denali: A machine learning potential for biological and organic chemistry with semi-empirical cost and DFT accuracy.

We present OrbNet Denali, a machine learning model for an electronic structure that is designed as a drop-in replacement for ground-state density functional theory (DFT) energy calculations. The model is a message-passing graph neural network that uses symmetry-adapted atomic orbital features from a low-cost quantum calculation to predict the energy of a molecule. OrbNet Denali is trained on a vast dataset of 2.3 × 106 DFT calculations on molecules and geometries. This dataset covers the most common elements in biochemistry and organic chemistry (H, Li, B, C, N, O, F, Na, Mg, Si, P, S, Cl, K, Ca, Br, and I) and charged molecules. OrbNet Denali is demonstrated on several well-established benchmark datasets, and we find that it provides accuracy that is on par with modern DFT methods while offering a speedup of up to three orders of magnitude. For the GMTKN55 benchmark set, OrbNet Denali achieves WTMAD-1 and WTMAD-2 scores of 7.19 and 9.84, on par with modern DFT functionals. For several GMTKN55 subsets, which contain chemical problems that are not present in the training set, OrbNet Denali produces a mean absolute error comparable to those of DFT methods. For the Hutchison conformer benchmark set, OrbNet Denali has a median correlation coefficient of R2 = 0.90 compared to the reference DLPNO-CCSD(T) calculation and R2 = 0.97 compared to the method used to generate the training data (ωB97X-D3/def2-TZVP), exceeding the performance of any other method with a similar cost. Similarly, the model reaches chemical accuracy for non-covalent interactions in the S66x10 dataset. For torsional profiles, OrbNet Denali reproduces the torsion profiles of ωB97X-D3/def2-TZVP with an average mean absolute error of 0.12 kcal/molfor the potential energy surfaces of the diverse fragments in the TorsionNet500 dataset.

Simulation and Computer Study of Structures and Physical Properties of Hydroxyapatite with Various Defects.

Simulation and computer studies of the structural and physical properties of hydroxyapatite (HAP) with different defects are presented in this review. HAP is a well-known material that is actively used in various fields of medicine, nanotechnology, and photocatalytic processes. However, all HAP samples have various defects and are still insufficiently studied. First of all, oxygen and OH group vacancies are important defects in HAP, which significantly affect its properties. The properties of HAP are also influenced by various substitutions of atoms in the HAP crystal lattice. The results of calculations by modern density functional theory methods of HAP structures with these different defects, primarily with oxygen and hydroxyl vacancies are analyzed in this review. The results obtained show that during the structural optimization of HAP with various defects, both the parameters of the crystallographic cells of the HAP change and the entire band structure of the HAP changes (changes in the band gap). This affects the electronic, optical, and elastic properties of HAP. The review considers the results of modeling and calculation of HAP containing various defects, the applied calculation methods, and the features of the effect of these defects on the properties of HAP, which is important for many practical applications.

Hydricity of 3d Transition Metal Complexes from Density Functional Theory: A Benchmarking Study.

A range of modern density functional theory (DFT) functionals have been benchmarked against experimentally determined metal hydride bond strengths for three first-row TM hydride complexes. Geometries were found to be produced sufficiently accurately with RI-BP86-D3(PCM)/def2-SVP and further single-point calculations with PBE0-D3(PCM)/def2-TZVP were found to reproduce the experimental hydricity accurately, with a mean absolute deviation of 1.4 kcal/mol for the complexes studied.

The temperature - pressure phase diagram of the calcite I - calcite II phase transition: A first-principles investigation

In this work, we use first-principles atomistic calculations based on density functional theory to investigate the first phase transition that occurs when pressure and temperature are applied to calcite I, the stable polymorph at standard temperature and pressure. The mechanism of this phase transition is identified as phonon softening, and the specific phonon mode is documented. The phase boundary is computed with the framework of the quasi-harmonic approximation (QHA) and compared to available experiments. The computed phase boundary is sensitive to the approximations adopted to describe electronic exchange and correlation. To explore this sensitivity a range of approximation with the framework of modern density functional theory have been used, namely; global hybrid exchange, the generalized gradient approximation and the inclusion of ad hoc corrections describing van der Waals interactions. The latter prove to be significant in improving the agreement with the available observations of phase stability. The phonon mediated nature of the transition suggests mechanisms for controlling the growth of calcite crystals, for example, via the inclusion of amino acids or partial substitution of ions, to frustrate displacements along the soft phonon modes.

Spherical tensor analysis of nuclear magnetic resonance signals for understanding chemical shielding tensors of DNA/RNA in gum cancer cells using group theory, MO analysis, and modern density–functional theory

Spherical tensor analysis of nuclear magnetic resonance signals for understanding chemical shielding tensors of DNA/RNA in gum cancer cells using group theory, MO analysis, and modern density–functional theory

Density-functional theory of material design: fundamentals and applications-I

Abstract This article is part-I of a review of density-functional theory (DFT) that is the most widely used method for calculating electronic structure of materials. The accuracy and ease of numerical implementation of DFT methods has resulted in its extensive use for materials design and discovery and has thus ushered in the new field of computational material science. In this article, we start with an introduction to Schrödinger equation and methods of its solutions. After presenting exact results for some well-known systems, difficulties encountered in solving the equation for interacting electrons are described. How these difficulties are handled using the variational principle for the energy to obtain approximate solutions of the Schrödinger equation is discussed. The resulting Hartree and Hartree–Fock theories are presented along with results they give for atomic and solid-state systems. We then describe Thomas–Fermi theory and its extensions which were the initial attempts to formulate many-electron problem in terms of electronic density of a system. Having described these theories, we introduce modern DFT by discussing Hohenberg–Kohn theorems that form its foundations. We then go on to discuss Kohn–Sham (KS) formulation of DFT in its exact form. Next, local density approximation (LDA) is introduced and solutions of KS equation for some representative systems, obtained using the LDA, are presented. We end part-I of the review describing the contents of part-II.

An improved seminumerical Coulomb and exchange algorithm for properties and excited states in modern density functional theory.

A seminumerical algorithm capable of performing large-scale (time-dependent) density functional theory (TD-DFT) calculations to extract excitation energies and other ground-state and excited-state properties is outlined. The algorithm uses seminumerical integral techniques for evaluating Coulomb and exchange parts for a set of density matrices as occurring in standard TD-DFT or similar methods for the evaluation of vibrational frequencies. A suitable optimized de-aliasing procedure is introduced. The latter does not depend on further auxiliary quantities and retains the symmetry of a given density matrix. The algorithm is self-contained and applicable to any orbital basis set available without the need for further auxiliary basis sets or optimized de-aliasing grids. Relativistic two-component excited-state TD-DFT calculations are reported for the first time using the developed seminumerical algorithm for standard and local hybrid density functional approximations. Errors are compared with the widely used "resolution of the identity" (RI) approximations for Coulomb (RI-J) and exchange integrals (RI-K). The fully seminumerical algorithm does not exhibit an enlarged error for standard DFT functionals compared to the RI approximation. For the more involved local hybrid functionals and within strong external fields, accuracy is even considerably improved.