Density Functional Calculation Method Research Articles

Density functional study of trans,trans,trans-[Pt(N3)2(OH)2(Py)2] on molecular structure and vibrational spectroscopy

This study records the selection of the best combination of geometric optimization and frequency calculation methods of the trans,trans,trans-[Pt(N3)2(OH)2(py)2](FM-190) by using different density functional calculation methods and basis sets. The results show that the CAM-B3LYP/SDD method has the best fit to the experimental data for geometric optimization, while the LSDA/SDD method has better performance in frequency calculation, and the infrared vibration peak is assigned. In addition, the calculated HOMO and LUMO show the energy gap and the internal charge transfer of this complex. The hyperconjugation of the pyridine ring have been explained by NBO analysis.

Highly Efficient Resolution-of-Identity Density Functional Theory Calculations on Central and Graphics Processing Units.

We present an efficient method to evaluate Coulomb potential matrices using the resolution of identity approximation and semilocal exchange-correlation potentials on central (CPU) and graphics processing units (GPU). The new GPU-based RI-algorithm shows a high performance and ensures the favorable scaling with increasing basis set size as the conventional CPU-based method. Furthermore, our method is based on the J-engine algorithm [White; , Head-Gordon, J. Chem. Phys. 1996, 7, 2620], which allows for further optimizations that also provide a significant improvement of the corresponding CPU-based algorithm. Due to the increased performance for the Coulomb evaluation, the calculation of the exchange-correlation potential of density functional theory on CPUs quickly becomes a bottleneck to the overall computational time. Hence, we also present a GPU-based algorithm to evaluate the exchange-correlation terms, which results in an overall high-performance method for density functional calculations. The algorithms to evaluate the potential and nuclear derivative terms are discussed, and their performance on CPUs and GPUs is demonstrated for illustrative calculations.

Probing the geometric and electronic structures of the lanthanide oxide HoOn–1/0 (n = 1–3) clusters

The complex 4f and 5d orbits of lanthanide oxide clusters increases the complexity and difficulty in both theoretical and experimental research. Combining the photoelectron imaging spectroscopy and ab initio calculations, the structural and electronic properties of HoO– were studied. The adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of HoO– have been measured to be 1.31(3) eV and 1.42(2) eV, respectively. To determine the vibrational structure and observed spectral bands in the photoelectron spectrum, Franck-Condon simulation of the ground-state transition for HoO– has been performed. The fundamental frequency of ground-state HoO is estimated to be 893 ± 73 cm−1. Density functional method (DFT) was used to study the neutral and anionic clusters of HoOn–1/0 (n = 1–3), and the most stable cluster structures were obtained. Based on the DFT calculations, the theoretical ADEs and VDEs of anionic HoOn– (n = 1–3) clusters were obtained and the photoelectron spectra (PES) of HoOn– (n = 1–3) clusters were simulated, which might stimulate further experimental investigations on the Ho oxide clusters. In addition, the corresponding molecular orbitals (MOs) were also discussed to reveal the interaction between Ho and O atoms. This study can help us to understand the chemical bonding in Ho-containing molecules and will provide some light in their surface chemistry and photochemistry investigation.

Thermochemistry and kinetics of the 2‐butanone‐4‐yl CH3C(=O)CH2CH2• + O2 reaction system

AbstractThermochemistry and kinetic pathways on the 2‐butanone‐4‐yl (CH3C(=O)CH2CH2•) + O2 reaction system are determined. Standard enthalpies, entropies, and heat capacities are evaluated using the G3MP2B3, G3, G3MP3, CBS‐QB3 ab initio methods, and the B3LYP/6‐311g(d,p) density functional calculation method. The CH3C(=O)CH2CH2• radical + O2 association reaction forms a chemically activated peroxy radical with 35 kcal mol−1 excess of energy. The chemically activated adduct can undergo RO−O bond dissociation, rearrangement via intramolecular hydrogen transfer reactions to form hydroperoxide‐alkyl radicals, or eliminate HO2 and OH. The hydroperoxide‐alkyl radical intermediates can undergo further reactions forming ketones, cyclic ethers, OH radicals, ketene, formaldehyde, or oxiranes. A relatively new path showing a low barrier and resulting in reactive product sets involves peroxy radical attack on a carbonyl carbon atom in a cyclic transition state structure. It is shown to be important in ketones when the cyclic transition state has five or more central atoms.

Benchmarking Density Functional Methods for Calculation of State Energies of First Row Spin-Crossover Molecules.

A systematic study of the performance of several density functional methodologies to study spin-crossover (SCO) on first row transition metal complexes is reported. All functionals have been tested against several mononuclear systems containing first row transition metal complexes and exhibiting spin-crossover. Among the tested functionals, the hybrid meta-GGA functional TPSSh with a triple-ζ basis set including polarization functions on all atoms provides the best results across different metals and oxidation states, and its performance in both predicting the correct ground state and the right energy window for SCO to occur is quite satisfactory. The effect of some additional contributions, such as zero-point energies, relativistic effects, and intramolecular dispersion interactions, has been analyzed. The reported strategy thus expands the use of the TPSSh functional to other metals and oxidation states other than FeII, making it the method of choice to study SCO in first row transition metal complexes. Additionally, the presented results validate the potential use of the TPSSh functional for virtual screening of new molecules with SCO, or its use in the study of the electronic structure of such systems.

Thermodynamic stability of Al11RE3 intermetallic compounds from first-principles calculations

Phase stability of Al-RE intermetallic compounds is crucial particularly for high temperature mechanical properties of Mg–Al–RE based alloys as well as the possibility of their commercial applications. For a long time, a controversial issue exists concerning whether Al11RE3 phase in heat-resistant Mg–Al–RE based alloys decomposes into Al2RE and Al when treated at high temperatures. Herein, we performed a systematically study to the relative phase stability of all Al11RE3 with single RE element compared with Al2RE at 0–1000K using the state-of-the-art first-principles density functional calculation method. The results indicate that Al11RE3 phases with RE=La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb are highly stable while those with RE=Ho, Er, Tm, Lu, Y, and Sc are always instable compared with the Al+Al2RE two-phase equilibrium at temperatures lower than 1000K. These calculations suggest that Al11RE3 phase in the Mg–Al–RE based alloys with Ce-rich misch metal or mixed RE elements would decompose into Al2RE and Al due to the instable Al11RE3 components, then decreased the alloy’s high temperature performances. The present work also provides important guidance for future optimization design of heat-resistant magnesium alloys.

Combinatorial experimental and DFT theoretical investigation over the formation mechanism of a binuclear phthalocyanine dimer

Herein, a density functional calculation method was used to explore the formation mechanism of a metal-free, homobinuclear phthalocyanine dimer.

Density Functional Study of Electronic, Magnetic and Chemical Bonding Properties of Spinel CdCr2O4

This paper is presented a theoretical study of electronic, magnetic and chemical bonding properties of spinel CdCr2O4 with a general formula of AB2X4 (A, B=transition- metal, X=oxides, chalcogenides) using density functional calculation method combined with spin- polarized theory within generalized gradient approximation. Density functional calculation is performed to observe the effects of magnetic ordering on the electronic and chemical bonding properties of spinel CdCr2O4 with both cubic and tetragonal structure from a pyrochlore lattice, using Quantum ESPRESSO package. Consequently, in order to investigate the magnetic properties in paramagnetic, ferromagnetic and antiferromagnetic orderings of spinel CdCr2O4, a first-principles study of the electronic structure as well as chemical bonding properties of spinel CdCr2O4 compound in two different structural form is performed: the cubic structure in order to investigate the desired properties in paramagnetic and ferromagnetic orderings, and tetragonal structure to calculate the same properties in antiferromagnetic ordering

THEORETICAL MODELING OF ELECTROCYCLIC 2 Н -PYRAN AND 2 Н -1,4-OXAZINE RING OPENING REACTIONS IN PHOTO- AND THERMOCHROMIC SPIROPYRANS AND SPIROOXAZINES

The detailed mechanism of thermal ring opening reactions of 2 H -pyran and 2 Н -1,4-oxazine systems in a broad range of spiropyran and spiro-1,4-oxazine derivatives was studied by density functional method calculations (PBE0/6-311+G(d,p)). The study revealed mechanistic features and the dependence of activation parameters of this electrocyclic reaction on the steric and electronic properties of spirofused rings in the studied compounds. Authors: Igor V. Dorogan*, Vladimir I. Minkin

Synthesis, spectroscopic properties and DFT study of (E)-1-[(3-(trifluoromethyl)phenylimino)methyl]naphthalen-2-olate

The Schiff base (E)-1-[(3-(trifluoromethyl)phenylimino)methyl]naphthalen-2-olate was synthesized from the reaction of 2-hydroxy-1-naphthaldehyde with 3-trifluoromethylaniline. The title compound has been characterized by FT-IR, UV-vis and X-ray single-crystal techniques. The present X-ray investigation shows that the compound exists in the zwitterionic form. Molecular geometry of the compound in the ground state have been calculated using the density functional method (DFT) with 6-31G(d,p) basis set and compared with the experimental data. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters. By using TD-DFT method electronic absorption spectra of the compound have been predicted and a good agreement with the TD-DFT method and experimental one is determined. In addition DFT calculations of the compound, molecular electrostatic potential (MEP), frontier molecular orbital analysis (HOMO-LUMO) and non-linear optical (NLO) properties were performed at B3LYP/6-31G(d,p).

Molecular structure and spectroscopic analysis of 1,4-Bis(1-methyl-2-benzimidazolyl)benzene; XRD, FT-IR, dispersive-Raman, NMR and DFT studies

This study reports the structural characterization of a bis-benzimidazole derivative, 1,4-Bis(1-methyl-2-benzimidazolyl)benzene (BMBB), by using spectroscopic and quantum chemical methods. The BMBB molecule was synthesized under microwave conditions and was characterized by using single-crystal X-ray diffraction, FT-IR, dispersive Raman and NMR spectroscopies. The potential energy surface scan study was carried out for the conformation of the theoretical structure. Quantum chemical calculations of relative energies, molecular geometry, vibrational wavenumbers, frontier molecular orbitals, atomic charges and gauge including atomic orbital (GIAO) 1H and 13C-NMR chemical shifts of the compound were carried out by using density functional method (DFT) at B3LYP/6-311++G(d,p) theory level. The complete assignments of the vibrational modes were performed with DFT calculations combined with scaled quantum mechanics force field (SQMFF) methodology. A satisfactory consistency between the experimental and theoretical findings was obtained. On account of the relative energies, population analysis and XRD results, the most stable conformational form of the molecule was also determined.

Experimental and density functional theory studies on ( E)-2-[(2-(hydroxymethyl)phenylimino)methyl]benzene-1,4-diol

The Schiff base compound ( E)-2-[(2-(hydroxymethyl)phenylimino)methyl]benzene-1,4-diol has been synthesized and characterized by 1H NMR, 13C NMR, IR, UV–Vis and single-crystal X-ray diffraction. Molecular geometry of the title compound in the ground state have been calculated using the density functional method (DFT) with 6-31G(d) basis set and compared with the experimental data. The calculated results show that the optimized geometry can well reproduce the crystal structure. By using TD-DFT method, electronic absorption spectra of the compound have been predicted and a good agreement with the TD-DFT method and experimental one is determined. The energetic behavior of the compound in solvent media has been examined using B3LYP method with the 6-31G(d) basis set by applying the polarizable continuum model (PCM). The total energy of the title compound decreases with increasing polarity of the solvent. In addition, DFT calculations of the compound, molecular electrostatic potential (MEP), natural bond orbital analysis (NBO) and non-linear optical (NLO) properties were performed at B3LYP/6-31G(d) level of theory.

Fully relativistic calculations of NMR shielding tensors using restricted magnetically balanced basis and gauge including atomic orbitals

A recently developed relativistic four-component density functional method for calculation of nuclear magnetic resonance (NMR) shielding tensors using restricted magnetically balanced basis sets for the small component (mDKS-RMB) was extended to incorporate the gauge including atomic orbitals (GIAO) approach. The combined method eliminates a strong dependence of the results, calculated with a finite basis set, on the choice of the gauge origin for the magnetic potential of a uniform external magnetic field. Benchmark relativistic calculations have been carried out for xenon dimer and the HX series (X=F, Cl, Br, I), where spin-orbit effects are known to be very pronounced for hydrogen shieldings. Our results clearly demonstrate that shieldings calculated at the four-component level with a common gauge (i.e., without GIAO, IGLO, or similar methods to treat the gauge problem) depend dramatically on the choice of the common gauge. The GIAO approach solves the problem in fully relativistic calculations as it does in the nonrelativistic case.

The hydrogen interaction in an FCC FePd alloy with a vacancy

The absorption of hydrogen in the ordered face-centered cubic FePd alloy is investigated using a density functional calculation method. Changes in the electronic structure and bonding after introducing an Fe or Pd vacancy are analysed. H locates close to a tetrahedral site and the H–metal bond is achieved at the expense of the interfacial Fe–Pd bond.

Effects of Si on the elastic property of Fe at Earth's inner core pressures: First principles study

We investigate the effects of silicon incorporation on the structural stability and elasticity of iron at the Earth's inner core pressures by means of the density functional calculation method in order to clarify the acceptability of silicon to the possible light elements dissolving in the inner core. Calculations show that (1) silicon incorporation enhances the bcc stability field as experimental understandings but hcp phase is the most stable at the inner core pressures even in Fe 0.875Si 0.125, (2) silicon less affects to the elasticity of bcc iron but decreases shear moduli of hcp and fcc phases, (3) it does not drastically change the elastic wave velocities of iron due to the cancellation of associated changes in density and elastic moduli, (4) both P and S wave velocities for each phase and compound linearly depend on the density, and (5) fcc phase is more elastically anisotropic than hcp phase and the anisotropy is enhanced by silicon. We apply two different high-temperature corrections to the wave velocities. Inner core P-wave velocity is well reproduced in the both models, whereas the calculated S-wave velocities significantly depend on the temperature correction. Small effects of silicon on the density–velocity relations are found in both models.

Gauge-invariant real-space method for density functional calculations in an external magnetic field

This paper describes a configuration-space method for ab initio electronic structure calculations in an arbitrarily strong external magnetic field. Special attention is paid to a manifestly gauge-invariant formulation of the problem that is independent of the discretization. We will show that rigorous gauge invariance can be implemented quite efficiently in real-space methods. To be able to reproduce empirical data for realistic systems, we also formulate our real-space algorithm in magnetic fields for nonlocal ionic pseudopotentials. Here, gauge invariance is again an issue, but has to be maintained by construction of such potentials. Numerical applications focus on two points. The first one is a careful assessment of the convergence properties of our algorithm and in particular the implications of our gauge-invariant formulation. We then calculate the magnetic susceptibilities and nuclear magnetic resonance shifts for a number of typical molecules of physical interest and compare with previous work.

Substitution Effect on Crystal Packings of Iodobenzonitriles and Iodophenols

The influence of iodine on the crystal packing of iodo-substituted benzonitriles (2−4) and phenols (5−7) was studied. To analyze the substituent effect, the series was completed, and the crystal structures of iodobenzene (1), m-iodobenzonitrile (3), m-iodophenol (6), and p-iodophenol (7) were determined. Ab initio density functional calculation methods were used to examine the energetic situation and dipole moments of the single molecules in all species.

Filtering a distribution simultaneously in real and Fourier space

We present a method to filter a distribution so that it is confined within a sphere of given radius r_c and, simultaneously, whose Fourier transform is optimally confined within a sphere of radius k_c. Our procedure may have several applications in the field of electronic structure methods, like the generation of optimized pseudopotentials and localized pseudocore charge distributions. As an example, we describe a particular application within the SIESTA method for density functional calculations, in removing the spurious rippling of the energy surface generated by the integrations in a real space grid.

Electronic structure and optical properties of binary skutterudite antimonides

The electronic structure near the Fermi level of binary skutterudite antimonides and optical properties are studied by the ab initio density functional calculation method. Lattice parameters of their compounds are determined by the calculation of the total energy by taking into account the spin-orbit interaction. The calculated band structure shows that lattice parameters strongly affect the band gap and the ordering of electronic states at $\ensuremath{\Gamma}$. ${\mathrm{CoSb}}_{3}$ is a narrow gap semiconductor with the band gap ${E}_{g}=118\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. Both ${\mathrm{RhSb}}_{3}$ and ${\mathrm{IrSb}}_{3}$ are zero-gap semiconductors, where in ${\mathrm{RhSb}}_{3}$ a conduction band and a valence band overlap slightly near $\ensuremath{\Gamma}$. Band structures near the gap on binary skutterudite antimonides can be represented by the four band model consisting of the two-band nonparabolic Kane model plus two parabolic bands. By using the band model the thermoelectric power for ${\mathrm{CoSb}}_{3}$ is calculated. The obtained electronic structure and the wave function are used to calculate and discuss interband optical absorption spectra and the x-ray absorption and emission near edge structure spectra. The calculated x-ray absorption (emission) near edge structure spectra are in good agreement with recent experimental data. Also the valence band density of states is shown to describe the experimental x-ray photoelectron spectra well.

Substituent effects on poly( p-phenylenevinylene) backbone, interrupted with silicon atoms: molecular orbital theory

The electronic structures and the structural deformations of silicon containing poly( p-phenylenevinylene) (PPV) polymers have been studied theoretically. The results of the calculations indicate that the regular π conjugated system is effectively interrupted by the organosilicon units yielding a blue emission. It has also been observed that substitution of methoxy on vinylene group caused significant structural deformation of the PPV lumophore, and subsequently, decreased the ionization potential (IP) and increased the electron affinity of the SiBu PPV. Experimentally, it is known that light emitting diodes made of silicon containing copolymers operate at low voltages, due to the reduction of the LUMO level in the luminescence polymers. The flat deformation of the PPV moiety induced a red shift of the absorption maxima. The substitution of phenyl ring on silicon atoms constrained free rotation around the Si C bond increasing the torsional angles of the lumophore and caused slight blue shift of absorption peak. Substitution of the cyano group on the vinylene moiety increased the ionization potential as well as the electron affinity. On the other hand, the electron donating methoxy group decreased the ionization potential and electron affinity. Those calculated results agree well with the experimental observations. The density functional calculation method, which account for electron correlation, yielded much more accurate values for the HOMO–LUMO gap than the Hartree–Fock method.