Version Of Density Functional Theory Research Articles

Quantum-Chemical Prediction of Molecular and Electronic Structure of Carbon-Nitrogen Chemical Compound with Unusual Ratio Atoms: C(N20).

Using various versions of quantum-chemical calculation, namely four versions of density functional theory (DFT), (DFT B3PW91/TZVP, DFT M06/TZVP, DFT B3PW91/Def2TZVP, and DFT M06/Def2TZVP) and two versions of the MP method (MP2/TZVP and MP3/TZVP), the existence possibility of the carbon-nitrogen-containing compound having an unusual M: nitrogen ratio of 1:20, unknown for these elements at present, was shown. Structural parameters data are presented; it was noted that, as may be expected, CN4 grouping has practically a tetrahedral structure, and the chemical bond lengths formed by nitrogen atoms and a carbon atom in the frameworks of each of the calculation methods indicated above are equal to each other. Thermodynamical parameters, NBO analysis data, and HOMO/LUMO images for this compound are also presented. A good agreement between the calculated data obtained using the above three quantum-chemical methods was noticed, too.

Twelve-Nitrogen-Atom Cyclic Structure Stabilized by 3d-Element Atoms: Quantum Chemical Modeling.

Using various versions of density functional theory (DFT), DFT M06/TZVP, DFT B3PW91/TZVP, DFT OPBE/TZVP, and, partially, the MP2 method, the possibility of the existence of 3d-element (M) compounds with nitrogen having unusual M: nitrogen ratio 1:12, unknown for these elements at the present, was shown. Structural parameter data were presented. It was shown that all MN4 groupings have tetragonal-pyramidal structure. It was noted that the bond lengths formed by nitrogen atoms and an M atom were equal to each other only in the case of M = Ti, V, Cr and Co, whereas for other Ms, they were slightly different; moreover, the bond angles formed by nitrogen atoms and an M atom were equal to 90.0°, or practically did not differ from this value. Thermodynamic parameters, NBO analysis data and HOMO/LUMO images for this compound were also presented. Good agreement between the calculated data obtained using the above three quantum chemical methods was also noted.

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

Absorption and emission properties of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (M = Al, Ga, In) and correlations with molecular electrostatic potential.

Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λF ) values whereas the effect is moderate at the absorption maximum (λabs ) values. The molecular electrostatic potential (MESP) at the metal center (VM ) and the most electron rich region indicated by MESP minimum (Vmin ), located at the oxygen of phenoxide ring exhibit excellent correlations with the λF and Stokes shift (λF -λabs ) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the Vmin or VM emerge as theoretical quantities to measure the same.

УДОСКОНАЛЕНИЙ МЕТОД ФУНКЦІЙ ГРІНА І ФУНКЦІОНАЛУ ГУСТИНИ У ВИЗНАЧЕННІ ВІБРАЦІЙНОЇ СТРУКТУРИ ФОТОЕЛЕКТРОННОГО СПЕКТРУ ДВОАТОМНИХ МОЛЕКУЛ

We present the optimized version of the hybrid combined density functional theory (DFT) and the Green’s-functions (GF) approach to quantitative treating the diatomic photoelectron spectra. The Fermi-liquid quasiparticle version of the density functional theory is used. The density of states, which describe the vibrational structure in photoelectron spectra, is defined with the use of combined DFT-GF approach and is well approximated by using only the first order coupling constants in the optimized one-quasiparticle approximation. Using the combined DFT-GF approach leads to significant simplification of the calculation and increasing an accuracy of theoretical prediction.

Performance of Density-Functional Tight-Binding in Comparison to Ab Initio and First-Principles Methods for Isomer Geometries and Energies of Glucose Epimers in Vacuo and Solution.

Density functional theory (DFT) is a widely used methodology for the computation of molecular and electronic structure, and we confirm that B3LYP and the high-level ab initio G3B3 method are in excellent agreement for the lowest-energy isomers of the 16 glucose epimers. Density-functional tight-binding (DFTB) is an approximate version of DFT with typically comparable accuracy that is 2 to 3 orders of magnitude faster, therefore generally very suitable for processing large numbers of complex structures. Conformational isomerism in sugars is well known to give rise to a large number of isomer structures. On the basis of a comprehensive study of glucose epimers in vacuo and aqueous solution, we found that the performance of DFTB is on par to B3LYP in terms of geometrical parameters excluding hydrogen bonds and isomer energies. However, DFTB underestimates both hydrogen bonding interactions as well as torsional barriers associated with rotations of the hydroxy groups, resulting in a counterintuitive overemphasis of hydrogen bonding in both gas phase as well as in water. Although the associated root mean squared deviation from B3LYP within epimer isomer groups is only on the order of 1 kcal/mol, this deviation affects the correct assignment of major isomer ordering, which span less than 10 kcal/mol. Both second- as well as third-order DFTB methods are exhibiting similar deviations from B3LYP. Even after the inclusion of empirical dispersion corrections in vacuum, these deviations remain for a large majority of isomer energies and geometries when compared to dispersion-corrected B3LYP.

Hybrid-Functional Calculations of the Copper Impurity in Silicon

Unsurprisingly, considering its significance to electronics, the impact of copper impurities on the electrical properties of silicon has been widely studied. Surprisingly, there is still marked disagreement, both among and between experiments and calculations. The remarkable disagreement between various theoretical studies is mainly due to the band-gap error in basic versions of density functional theory. This study revisits the problem using the nuanced HSE06 hybrid functional. Its model for the electronic structure of Cu in Si yields results that agree well with experimental transition levels and solubilities.

A study of the valence shell electronic states of s-triazine by photoabsorption spectroscopy and ab initio calculations

The absolute photoabsorption cross section of s-triazine has been measured between 4 and 40eV, and is dominated by bands associated with valence states. Structure due to Rydberg excitations is both weak and irregular. Jahn-Teller interactions affect the vibronic structure observed in the Rydberg absorption bands due to excitation from the 1e″ or 6e′ orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled cluster linear response approach. The theoretical studies indicate that Rydberg/Rydberg and Rydberg/valence mixing is important.

Density Functional Methods for Fast Screening of Metal–Organic Frameworks for Hydrogen Storage

Classical density functional theory (DFT) has been routinely used for the characterization of pore size distribution and specific surface area of porous materials by gas physisorption. However, its application to large-scale screening of materials for gas storage has been largely unexplored because it is commonly believed that the DFT calculations are applicable only to one-dimensional systems and highly sensitive to the approximations introduced in the free-energy functionals. In this work, we have investigated four representative versions of nonlocal density functionals for predicting H2 adsorption using both the slit pore model and a large library of metal–organic frameworks (MOFs) under a broad range of temperatures and pressures. The four versions of DFT share a common functional from the modified fundamental measure theory to account for the molecular excluded volume effects while differing in their approximations to represent the intermolecular attractions, viz., mean-field approximation, two versi...

Theoretical investigation of the borazine-melamine polymer as a novel candidate for hydrogen storage applications.

Ab initio calculations and molecular dynamic simulation were employed to study the interaction of molecular hydrogen with the borazine-melamine polymer (BMP) in order to explore its potential for hydrogen storage applications. The calculations were performed using the long range corrected version of density functional theory, the Coulomb-attenuating method (CAM-B3LYP) and the second order Møller-Plesset perturbation theory (MP2). The results showed that the average adsorption energy per hydrogen is about -0.7 and -0.3 kcal mol(-1) at the MP2/6-311+G(d,p) and CAMB3LYP/6-311+G(d,p) levels of theory, respectively. The adsorption energies were corrected for the basis set superposition error (BSSE) by the counterpoise method. It was found that the hydrogen storage capacity of the BMP is about 6.49 wt%, which is close to the values reported for the other selected materials for the hydrogen storage in the literature. The maximum number of hydrogen molecules, which were adsorbed by the BMP building block, is about ten. Molecular dynamic simulation was performed to assess the potential of BMP for hydrogen storage.

A study of the valence shell electronic states of pyridazine by photoabsorption spectroscopy and time-dependent density functional theory calculations

The valence shell electronic states of pyridazine have been studied experimentally, by recording the photoabsorption spectrum, and theoretically, by calculating oscillator strengths and excitation energies. The absolute photoabsorption cross section has been measured between 4 and 40 eV, using synchrotron radiation, and is dominated by prominent bands associated with intravalence transitions. In contrast, structure due to Rydberg excitations is weak. One Rydberg state, belonging to a series converging onto the state limit has been observed and assigned. The accompanying vibrational structure has been characterized by analogy with that in the corresponding photoelectron band. Vibrational progressions associated with Rydberg states belonging to one or more series converging onto the state limit have also been observed. The absorption structure associated with these series is complex and only tentative assignments have been proposed for the Rydberg states. The time-dependent version of density functional theory has been used to calculate oscillator strengths and excitation energies for the optically allowed singlet–singlet valence transitions and also to obtain the excitation energies for electric-dipole-forbidden and/or spin-forbidden transitions. The valence shell photoionization dynamics have been investigated theoretically by calculating photoelectron angular distributions and photoionization partial cross sections of the four outermost orbitals. In addition, the ground state outer valence electronic configuration has been obtained at the complete active space self-consistent field and the N-electron valence state perturbation theory to second-order levels of theory.

Nature of Noncovalent Interactions in Catenane Supramolecular Complexes: Calibrating the MM3 Force Field with ab Initio, DFT, and SAPT Methods

The design and assembly of mechanically interlocked molecules, such as catenanes and rotaxanes, are dictated by various types of noncovalent interactions. In particular, [C-H···O] hydrogen-bonding and π-π stacking interactions in these supramolecular complexes have been identified as important noncovalent interactions. With this in mind, we examined the [3]catenane 2·4PF6 using molecular mechanics (MM3), ab initio methods (HF, MP2), several versions of density functional theory (DFT) (B3LYP, M0X), and the dispersion-corrected method DFT-D3. Symmetry adapted perturbation theory (DFT-SAPT) provides the highest level of theory considered, and we use the DFT-SAPT results both to calibrate the other electronic structure methods, and the empirical potential MM3 force field that is often used to describe larger catenane and rotaxane structures where [C-H···O] hydrogen-bonding and π-π stacking interactions play a role. Our results indicate that the MM3 calculated complexation energies agree qualitatively with the energetic ordering from DFT-SAPT calculations with an aug-cc-pVTZ basis, both for structures dominated by [C-H···O] hydrogen-bonding and π-π stacking interactions. When the DFT-SAPT energies are decomposed into components, we find that electrostatic interactions dominate the [C-H···O] hydrogen-bonding interactions, while dispersion makes a significant contribution to π-π stacking. Another important conclusion is that DFT-D3 based on M06 or M06-2X provides interaction energies that are in near-quantitative agreement with DFT-SAPT. DFT results without the D3 correction have important differences compared to DFT-SAPT, while HF and even MP2 results are in poor agreement with DFT-SAPT.

A non-perturbative approach to freezing of superfuid 4He in density functional theory

Freezing of various classical liquids is successfully described by density functional theory (DFT). On the other hand, so far no report has been published that DFT describes the freezing of superfuid 4He correctly. In fact, DFT gives too stable solid phase and the superfuid phase does not exist at finite positive pressures within a second order perturbation. In this paper we try a non-perturbative version of DFT, that is modified weighted density approximation (MWDA) to go beyond second order perturbation for the freezing of superfuid 4He. Via an exact zero temperature quantum Monte-Carlo (QMC) method we have computed the equation of state and the compressibility of superfuid 4He. By utilizing a recently introduced analytic continuation method (the GIFT method), we have obtained also density response functions at different densities from QMC imaginary time correlation functions. Contrary to second order perturbation, by employing these QMC data as DFT input we find a too stable superfuid phase, preventing freezing around the experimentally observed freezing pressure. We find the same pathological behavior by using another model energy functional of superfuid 4He (Orsay-Trento model). We conclude that the straightforward MWDA calculation gives such a poor result when liquid-gas transition is present.

Invariant imbedding theory of charge pumping in quantum wires

We have developed a method to study the theory of charge pumping through a continuous quantum wire using the invariant imbedding approach. Using this method, the general properties of quantum charge pumping, with and without inclusion of many-body interactions are investigated. Using the invariant imbedding approach allows us to address directly the complex reflection (R) and transmission (T) matrices across the wire instead of considering the spectrum of the Schrodinger equation. Using the Kohn–Sham version of density functional theory (DFT), the many-body interactions in the quantum wire is investigated. We calculated the pumped current in those two cases. In the case of ignoring the many-body effects, the pumped current depends on the width of the driven potential barriers and in the case of nonequality of the width of barriers, our study predicts a nonzero charge pumping at the phase difference φ=0 even when the driving potentials are equal. In the second case, although the pumped current had sinusoidal dependence on φ but its value significantly decreased and we also observed nonzero pumping at φ=0 even when the driving potentials and their widths are equal, which is consistent with the recent experimental result.

A study of the valence shell electronic states of pyrimidine and pyrazine by photoabsorption spectroscopy and time-dependent density functional theory calculations

The valence shell electronic states of pyrimidine and pyrazine have been studied experimentally and theoretically. The absolute photoabsorption cross sections have been measured between 4 and 40 eV, using synchrotron radiation, and are dominated by prominent bands associated with intravalence transitions. In contrast, the structure due to Rydberg excitations is weak, but series have been observed converging onto the or limits in pyrimidine and the or limits in pyrazine. A comparison between the photoabsorption spectrum of pyrazine-h4 and that for pyrazine-d4, together with calculated transition energies, has helped clarify the assignments of the 6ag→npb1u and npb2u Rydberg series. The vibrational progressions associated with these states have been assigned through analogy with those in the corresponding photoelectron band. The time-dependent version of density functional theory has been used to calculate oscillator strengths and excitation energies for the optically allowed singlet–singlet valence transitions, and also to obtain the excitation energies for electric-dipole-forbidden and/or spin-forbidden transitions. These theoretical results have allowed many of the experimentally observed bands to be assigned and provide a generally satisfactory description of the valence shell photoabsorption spectrum. Several of the prominent bands appearing above the ionization threshold can be correlated with predicted intense intravalence transitions.

Theoretical and spectroscopic study of ethyl 1,4-dihydro-4-oxoquinoline-3-carboxylate and its 6-fluoro and 8-nitro derivatives in neutral and radical anion forms

A systematic comparative theoretical and spectroscopic study has been performed on a series of four recently prepared ethyl 4-oxoquinoline-3-carboxylate derivatives possessing a variety of biological activities. The most probable oxo- and hydroxy-tautomeric neutral molecular forms were identified using density functional theory (DFT). Vertical optical transitions were calculated for global minima using time-dependent version of DFT. Calculated spectra were compared with the experimental electronic spectra of quinolones measured in various aprotic solvents (toluene, acetonitrile, dimethylsulfoxide). Finally, the structures and spin density distributions of radical anions obtained upon photoinduced reduction of two nitro-substituted derivatives in titania suspension were deduced from the comparison of calculated isotropic hyperfine coupling constants with experimental data determined from EPR spectra.

Photochemical Water Decomposition in the Troposphere: DFT Study with a Symmetrized Kohn–Sham Formalism

Photochemical reaction of the electronically excited NO(2)* species with the water molecule is studied in terms of a new version of density functional theory by selecting the specific (2)A'' symmetry of the whole system, which is different from the ground-state pattern. The excited C(2)A(2) state of the NO(2) molecule is found to be distorted to the equilibrium structure O=N-O(.), which poses the (2)A'' symmetry in the C(s) point group. With the B3LYP functional it is shown that such an electronically excited NO(2)* molecule, generated by visible light (λ=420 nm), can react with water vapor to produce OH+HONO species, an important source of tropospheric hydroxyl radicals. This photochemical process can be considered as a possible mechanism of atmosphere self-cleaning.

Derivation of dynamical density functional theory using the projection operator technique

Density functional theory is a particular case of a general theory of conjugate variables that serves as the basis of the projection operator technique. By using this technique we derive a general dynamical version of density functional theory which involves a generalized diffusion tensor. The diffusion tensor is given by a Green-Kubo expression. For Brownian dynamics of dilute colloidal suspensions, the standard dynamical density functional theory is recovered.

Spin-density wave in Cr: Nesting versus low-lying thermal excitations

It is well known that present versions of density functional theory do not predict the experimentally observed spin-density wave state to be the ground state of Cr. Recently, a so-called ``nodon model'' has been proposed as an alternative way to reconcile theory and experiment: the ground state of Cr is truly antiferromagnetic, and the spin-density wave appears due to low-lying thermal excitations (``nodons''). We examine in this paper whether the postulated properties of these nodons are reproduced by ab initio calculations.

Supercell Band Calculations and Correlation for High- Copper Oxide Superconductors

First principle band calculations based on local versions of density functional theory (DFT), together with results from nearly free-electron models, can describe many typical but unusual properties of the high- copper oxides. The methods and a few of the most important results are reviewed. Some additional calculations are presented, and the problems with the commonly used approximate versions of DFT for oxides are discussed with a few ideas for corrections. It is concluded that rather modest corrections to the approximate DFT, without particular assumptions about strong correlation, can push the ground state towards antiferro magnetic (AFM) order. Spin fluctuations interacting with phonons are crucial for the mechanism of superconductivity in this scenario.