A theoretical investigation on the electronic structures and phosphorescent properties of three heteroleptic iridium(III) complexes with different substituted ancillary groups

Three heteroleptic iridium(III) complexes 1, 2 and 3 bearing two cyclometalating 2′,6′-difluoro-2,3′-bipyridyl (dfpypy) chelates and one pyridyl pyrazolate ligand have been investigated by using the density functional theory/time-dependent density functional theory method to study the influence of the different substituent groups (―CF₃ and ―N(CH₃)₂ moiety on the electronic structures, phosphorescent properties and the organic light-emitting diode performance. The lowest energy absorption wavelength calculated is in good agreement with the experimental value. The lowest energy emissions of complexes 1, 2 and 3 are localised at 454, 534 and 821 nm, respectively. Ionisation potential and electron affinity have been calculated to evaluate the injection abilities of holes and electrons into these complexes. The calculated results show that the different substitute groups affect the charge transfer rate and balance. Finally, we hope that this study can provide a good guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes.     

Density functional theory study on the structural properties and energetics of microclusters

Density functional theory calculations with B3LYP exchange-correlation functional using CEP-121G basis set have been carried out in order to elucidate the structural properties and energetics of neutral zinc telluride clusters, Zn_mTe_n (m+n6), in their ground states. The geometric structures, binding energies, vibrational frequencies and infrared intensities, Mulliken charges on atoms, HOMO and LUMO energies, the most possible dissociation channels and their corresponding energies for the clusters have been considered.     

Computational studies of CO and CO: Density functional theory and time-dependent density functional theory

Potential energy curves, equilibrium interatomic distances, term energies and harmonic vibration frequencies for the 16 lowest states of neutral carbon monoxide and the six lowest states of singly ionized carbon monoxide are calculated by density functional theory (DFT) and linear-response time-dependent density functional (LR-TDDFT) theory. The results are compared with experimental data. The two theories, DFT and LR-TDDFT, are described briefly.     

Electronic and magnetic properties of single 3d-transition metals adsorbed on anthracene: a relativistic density functional theory study

Within the framework of relativistic density functional theory in the regime of generalised gradient approximation, we have obtained magnetic properties of single 3d-transition metal atoms (from Sc to Ni) adsorbed on anthracene molecule. Binding energies, local spin and orbital magnetic moments, and magnetic anisotropy energies were determined. Our calculations show that all 3d-transition metal atoms bind to anthracene molecule in the presence of spin–orbit coupling. We have found these complexes are spin-polarised and soft magnet.     

Electronic and magnetic properties of Pd-Ni multilayers: Study using density functional theory

Electronic and magnetic properties of Pd-Ni multilayers have been studied using VASP method in the framework of the density functional theory (DFT). The calculations performed for different configurations (Pd_n/Ni_m(1 1 1), where n Pd layers are piled up over m Ni layers with n=0 to 4 and n+m=4), reveal that the important magnetic moment of Ni is significantly enhanced according as n increases due to hybridization effects between Pd and Ni mostly localized at the interface. The results also indicate that the Pd atoms are strongly polarized in the studied systems when compared with the pure metal.     

Optical properties of clusters and molecules from real-time time-dependent density functional theory using a self-consistent field

We present a detailed study of optical absorption spectra of finite-size structures, using a method based on time-dependent density-functional theory (TDDFT), which involves a self-consistent field for the propagation of the Kohn–Sham wavefunctions in real-time. Although our approach does not provide a straightforward assignment of absorption features to corresponding transitions between Kohn–Sham orbitals, as is the case in frequency-domain TDDFT methods, it allows the use of larger timesteps while conserving total energy and maintaining stable dipole moment oscillations. These features enable us to study larger systems more efficiently. We demonstrate the efficiency of our method by applying it to a hydrogen-terminated silicon cluster consisting of 364 atoms, with and without P impurities. For cases where direct comparison to experiment can be made, we reproduce the absorption features of fifteen small molecules [N₂, O₂, O₃, NO₂, N₂O, NH₃, H₂O, H₂CO, H₂CO₃, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₆H₆] and find generally good agreement with experimental measurements. Our results are useful for the detection and the determination of orientation of these molecules.     

Piperidine adsorption on two different silver electrodes: A combined surface enhanced Raman spectroscopy and density functional theory study

The surface enhanced Raman scattering (SERS) spectra of piperidine in silver colloid solution, on roughened silver electrode and on roughened silver electrode modified with silver nanoparticles were studied, and the high-quality SERS spectra of piperidine on roughened silver electrode modified with silver nanoparticles were obtained for the first time. Surface selection rules derived from the EM enhancement model were employed to deduce piperidine orientations on the different surfaces. On the basis of this, two models of piperidine adsorbed on the surface of the silver nanoparticles were built, and DFT-B3PW91/LanL2dz was applied to calculate the Raman frequencies. It proves that, at higher potential values, the piperidine is perpendicularly standing on the roughened silver electrode surface though its lone-electron pair, but in silver colloid solution and on the silver nanoparticles modified silver electrode the piperidine molecular lies flat on the silver surface. In the meantime, the potential dependent SERS of piperidine on the modified electrode were studied.     

First-principles density functional theory study of generalized stacking faults in TiN and MgO

In this paper, the generalized stacking fault (GSF) energies in different slip planes of TiN and MgO are calculated using highly reliable first-principles density functional theory (DFT) calculations. During DFT calculations, the issue of different ways to calculate the GSF energetics in ceramic materials containing more than one element was addressed and applied. For 〈1?1?0〉/{1?1?1} slip, a splitting of saddle point in TiN was observed. For 〈1?1?2〉/{1?1?1} slip, a stable stacking fault at a₀/3〈1?1?2〉 displacement was formed in TiN. For synchroshear mechanism where the slip was accompanied by a cooperative motion of the interfacial nitrogen atoms within the slip plane, a second stable stacking fault was formed at a₀/6〈1?1?2〉 displacement. The energy barrier for the shuffling of nitrogen atoms from one state to another is calculated to be 0.70 eV per atom. In contrast, such features are absent in MgO. These differences highlight the influence of complex bonding nature (mixed covalent, ionic, and metallic bondings) of TiN, which is substantially different than that in MgO (simple ionic bonding) on GSF shapes.     

Theoretical study on the electronic structures and phosphorescent properties of four Ir(III) complexes with different substituents on the ancillary ligand

The geometry structures, electronic structures, absorption and phosphorescent properties of four Ir(III) complexes {[(F₂-ppy)₂Ir(pta-X)], where F₂-ppy = (2,4-difluoro)phenylpyridine; pta = pyridine-1,2,4-triazole; X = –CF₃; –H; –CH₃; –N(CH₃)₂}, are investigated using the density functional method. The results reveal that the electron-accepting group –CF₃ has no obvious effect on absorption and emission properties, while the substitutive group –N(CH₃)₂ with strong electron-donating ability has obvious effect on the emission properties. The mobility of hole and electron were studied computationally based on the Marcus–Hush theory. Calculations of ionisation potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. We hope that this theoretical work can provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes.     

A series of copper(I) complexes with electron donor/acceptor embedded ligands: Synthesis, photophysical and electroluminescent properties

In this paper, we report the synthesis of four diimine ligands incorporated with an electron donor/acceptor, as well as their corresponding Cu(I) complexes with bis(2-(diphenylphosphanyl)phenyl) ether as an ancillary ligand, resulting in four phosphorescent Cu(I) complexes. Their crystal structures as well as photophysical and thermal properties are discussed in detail. Experimental data and theoretical calculations confirm that electron donor moieties and limited conjugation system may self-restrict geometry relaxation in excited states, leading to narrowed and blue-shifted emission bands. On the other hand, electron acceptor moieties and large coplanar conjugation system are ineffective in restricting geometry relaxation, leading to broadened and red-shifted emission bands. However, the introduction of electron donors compromises thermal stability of Cu(I) complexes. We also explore one of the Cu(I) complexes as a dopant for electroluminescence application, and a maximum luminance of 680 cd/m² peaking at 620 nm is achieved.     

Structural and magnetic properties of double-perovskite Ba2MnMoO6 by density functional theory

Perovskite-like materials which include magnetic elements have relevance due to the technological perspectives in the spintronics industry. In this work, we report the studies of Ba₂MnMoO₆ material by using the density functional theory. The interchange-correlation potential was included through the generalized gradient approximation. Our structural calculations are in agreement with the experimental results which show that the material crystallizes in the 225 space group (Fm3¯m) and has a lattice parameter of about 8070 Å. The density of states study was carried out by considering the up and down spin orientations. Results show that Ba₂MnMoO₆ has a conductor behavior due to dominant Mn spin-up and Mo spin-down contributions. The magnetic moment was calculated to be 2.9 μ_B.     

Effect of boron and nitrogen co-doping on CNT's electrical properties: Density functional theory

In this work, we have theoretically studied the changes in electrical properties of three different geometrical structures of carbon nanotubes upon co-doping them with boron and nitrogen atoms. We applied different doping mechanisms to study band structure variations in the doped structures. Doping carbon nanotubes with different atoms will create new band levels in the band structure and as a consequence, a shift in the Fermi level occurs. Whereas, filling up the lowest conduction/ upper valence bands created an up/ downshift in the Fermi level. Moreover, dopants concentration and dopants position play a critical rule in defining the number of new band levels. These new band levels in the band gap region represented as new peaks appeared in the density of states. These new bands are solely attributed to co-doping carbon nanotubes with boron and nitrogen atoms.     

Photophysical properties of a series of high luminescent europium complexes with fluorinated ligands

A series of high luminescent europium complexes have been synthesized, such as Eu(TFNB)₃phen (1), Eu(PFNP)₃phen (2), Eu(HFNH)₃phen (3) and Eu(PFND)₃phen (4), which have β-diketone ligands containing fluorinated alkyl chains with different lengths and conjugated naphthyl groups, i.e., 4,4,4-trifluoro-1-(2-naphthyl)butane-1,3-dione (TFNB); 4,4,5,5,5-pentafluoro-1-(2-naphthyl)pentane-1,3-dione (PFNP); 4,4,5,5,6,6,6-heptafluoro-1-(2-naphthyl)hexane-1,3-dione (HFNH) and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-pentadecafluoro-1-(2-naphthyl)decane-1,3-dione (PFND). And 10-phenanthroline (phen) is coordinated as the neutral second ligand in 1-4. The crystal structures of 1 and 2 have been studied, which are typical and similar to that of 3. The results of TGA-DTA suggest that these Eu complexes have good thermal stabilities. By means of absorption and (time resolved) emission spectroscopy including determination of luminescence quantum yields, energy transfer dynamics and so on, the following results have been obtained: first, these Eu complexes show characteristic pure red color photoluminescence emission with high quantum efficiencies from the central Eu³⁺ ions through the excitation of the ligands; secondly, photophysical properties of 1, 2, 3 and 4, especially the lifetimes of excited states ⁵D₀ of Eu³⁺ ions and quantum efficiencies are influenced by the different lengths of fluorinated alkyl chains, though the singlets (S₁) and triplets (T₁) of the fluorinated ligands are almost the same.     

Investigation of photophysical properties of mer-tris(8-hydroxyquinolinato) aluminum (III) and its derivatives: DFT and TD-DFTcalculations

Optimized structures and photophysical properties of mer- and fac-Alq₃ have been generated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Investigating the substitution effect in the Alq₃ derivatives, the role of the electron-donating (CH₃- and NH₂-) and electron-withdrawing (F-, CN-, NO₂- and phenyl-) groups with 2- to 7-substitution have been analyzed. According to the calculation results, the 4- and 5- substituted Alq₃ exhibit an apparent spectral shift relative to the non-substituted Alq₃. The HOMO, LUMO, E_g (the energy gap between LUMO and HOMO), (maximum absorption wavelength) and f (the relative oscillator strength) of mer-Alq₃ with the 4- or 5-phenyl substitution on the quinoline ligand in the ground electronic state were calculated by using the DFT/B3LYP/6-31G(d) and TD-DFT methods. 5-phenyl substituted mer-Alq₃ with an electron-donating substituent showed an increase in the π-delocalization as compared to the 4-phenyl substituted mer-Alq₃ derivatives. Similarly, 4-phenyl substituted mer-Alq₃ with electron-withdrawing substituents also exhibits increased π-delocalization in the pyridine ring as compared to the non-substituted Alq₃. Replacing the CH group at the 4, 5 and 4,5 positions of the quinoline ligand of mer-Alq₃ with the aza group (nitrogen atom) gives three Alq₃ analogous: AlX₃, Al(NQ)₃ and Al(NX)₃; the calculated energy gap E_g of these derivatives decreases in the order Al(NQ)₃>Al(NX)₃>AX₃. Four quinoline with group III metals Mq₃ complexes were investigated for the photophysical properties; the calculated energy gap E_g decreases in the order Tlq₃>Inq₃>Gaq₃>Alq₃. The photophysical properties of 4-hydroxy-8-methyl-1,5-naphthyridine (mND) chelated with group III metals (MmND₃ complexes) were investigated also; their calculated E_g have the opposite order as those of Mq₃ complexes.     

Density functional theory study on antiferromagnetic interactions in a silver (I) complex of nitronyl nitroxide

A one-dimensional (1D) silver (I) complex of nitronyl nitroxide with fairly strong antiferromagnetic interaction, in which the metal ions are diamagnetic, is investigated by means of the ab initio crystal orbital method based on the density functional theory. The calculated values of the magnetic coupling constant (J) are close to the experimental measured J value in the periodic system. The magneto-structural correlation reveals that the existence of an antiferromagnetic coupling pathway along nitronyl nitroxide units via silver (I) ion in this system. The spin population distribution also shows the existence of spin delocalization along the ONCNO–Ag–ONCNO, which affords a rational interpretation for the antiferromagnetic interaction mechanism.     

Structural,elastic, electronic,andoptical properties of layered TiNX (X = F,Cl, Br,I) compounds: a density functional theory study

ABSTRACT

Titanium nitride halides, TiNX (X = F, Cl, Br, I) in the α-phase (orthorhombic) are exciting quasi two-dimensional (2D) electronic systems exhibiting a fascinating series of electronic ground states. Pristine TiNX are semiconductors with varying energy gaps and possess attractive properties for potential applications in optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated TiNCl becomes superconducting at reasonably high temperature. We have revisited the electronic band structure of TiNX using density functional theory (DFT) based calculations. The atomic orbital resolved partial electronic energy densities of states are calculated together with the total density of states (TDOS). The structural and elastic properties have been investigated in details for the first time. The elastic anisotropy has been explored. The optical properties of TiNX are studied for the first time. The Debye temperatures have been calculated and the related thermal and phonon parameters are discussed. The calculated physical parameters are compared with existing theoretical and experimental results and showed fair agreement. TiNX are found to reflect electromagnetic radiation strongly in the mid ultraviolet region. The elastic properties show high degree of anisotropy. The effect of halogen atoms on various structural, elastic, electronic, and thermal properties in TiNX are also discussed in detail.     

Hydrogen storage in BC3 composite single-walled nanotube:a combined density functional theory and Monte Carlo investigation

This paper applies a density functional theory(DFT) and grand canonical Monte Carlo simulations(GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC 3 nanotubes and carbon nanotubes.The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes.Furthermore,the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions.The present results have shown that with both computational methods,the hydrogen storage capacity of BC 3 nanotubes is superior to that of carbon nanotubes.The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.