Excited states of OsO4: A comprehensive time‐dependent relativistic density functional theory study

A large number of scalar as well as spinor excited states of OsO₄, in the experimentally accessible energy range of 3–11 eV, have been captured by time‐dependent relativistic density functional linear response theory based on an exact two‐component Hamiltonian resulting from the symmetrized elimination of the small component. The results are grossly in good agreement with those by the singles and doubles coupled‐cluster linear response theory in conjunction with relativistic effective core potentials. The simulated‐excitation spectrum is also in line with the available experiment. Furthermore, combined with detailed analysis of the excited states, the nature of the observed optical transitions is clearly elucidated. It is found that a few scalar states of ³T₁ and ³T₂ symmetries are split significantly by the spin‐orbit coupling. The possible source for the substantial spin‐orbit splittings of ligand molecular orbitals is carefully examined, leading to a new interpretation on the primary valence photoelectron ionization spectrum of OsO₄. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Time‐dependent local‐density approximation in real time: Application to conjugated molecules

The time‐dependent local‐density approximation (TDLDA) is applied to the optical response of conjugated carbon molecules in the energy range of 0–30 eV, with calculations given for carbon chains, polyenes, retinal, benzene, and C₆₀. The major feature of the spectra, the collective π–π* transition, is seen at energies ranging from below 2 to 7 eV and is reproduced by the theory to a few tenths of an electron volt with a good account of systematic trends. However, there is some indication that TDLDA predicts too much fragmentation of the strength function in large molecules. Transition strengths are reproduced with a typical accuracy of 20%. The theory also predicts a broad absorption peak in the range of 15–25 eV, and this feature agrees with experiment in the one case where quantitative data is available (benzene). ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 55–66, 1999     

Time‐dependent density functional theory study of electronic spectrum property for carbazolyl–pyridinyl alternating copolymers

Three A‐B‐type fluorescent copolymers comprised of alternating carbazolyl and pyridinyl units, poly[(2,7‐(N‐(2‐ethylhexyl)carbazolyl)‐alt‐(3,5‐pyridinyl))](PEHCP‐35), poly[(2,7‐(N‐(2‐ethylhexyl)carbazolyl)‐alt‐(2,6‐pyridinyl))] (PEHCP‐26) and poly[(2,7‐(N‐(2‐ethyl‐hexyl)carbazolyl)‐alt‐(2,5‐pyridinyl))] (PEHCP‐25), are studied by means of the density functional theory (DFT/B3LYP/6‐31G). Based on the optimized geometries, the optical properties are calculated by employing time‐dependent density functional theory (TD‐DFT). The bandgaps and optical properties are saturated quickly in PEHCP‐35 and PEHCP‐26. It is known from experiment that PEHCP‐25 is actually an oligomer with a polymerization degree of 4. So the tetramers of PEHCP‐35, PEHCP‐26, and PEHCP‐25 are adopted to study the electronic and optical properties, and the calculated results are in close agreement with experiment. The calculated bandgaps of copolymers obtained from two ways, i.e., HOMO–LUMO gaps and the lowest excitation energies, decrease in the following order PEHCP‐35 > PEHCP‐26 > PEHCP‐25, the same trend as the data obtained from the edge of the electric band but different from the electrochemically obtained data from experiment (PEHCP‐25 > PEHCP‐26 > PEHCP‐35). The outcomes showed that, when excited, a charge transfer from carbazolyl unit to pyridinyl unit occurs, and the lumophor is mainly carbazolyl units. The UV absorption and emission wavelengths both exhibit bathochromic shifts: PEHCP‐35 < PEHCP‐26 < PEHCP‐25. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electronic structure and spectroscopic properties of 6‐aminophenanthridine and its derivatives: Insights from density functional theory

6‐Aminophenanthridine (6AP) and its derivatives show important biological activities as antiprion compounds and inhibitors of the protein folding activity of the ribosome. Both of these activities depend on the RNA binding property of these compounds, which has been recently characterized by fluorescence spectroscopy. Hence, fundamental insights into the photophysical properties of 6AP compounds are highly important to understand their biological activities. In this work, we have calculated electronic structures and optical properties of 6AP and its three derivatives 6AP8CF₃, 6AP8Cl, and 6APi by density functional theory (DFT) and time‐dependent density functional theory (TDDFT). Our calculated spectra show a good agreement with the experimental absorption and fluorescence spectra, and thus, provide deep insights into the optical properties of the compounds. Furthermore, comparing the results obtained with four different hybrid functionals, we demonstrate that the accuracy of the functionals varies in the order B3LYP > PBE0 > M062X > M06HF. © 2015 Wiley Periodicals, Inc.     

Non‐born–oppenheimer density functional theory for excited states by using green's function techniques

We have proposed a numerical scheme for the non‐Born–Oppenheimer density functional calculation based upon the Green function techniques within the GW approximation for evaluating quasiparticle excitations of the electronic and nuclear motion in the full quantum mechanical treatment. We calculate the excitation energy and the orbital energy of a hydrogen molecule, a muon molecule, and a positronium–hydrogen complex within the treatment of the dynamical screening. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 354–362, 2001     

Analysis of XPS valence band spectra of polymers using a density‐functional theory based calculation of model oligomers

XPS valence band spectra of 10 polymers (PE, PcI, PPG, PVME, PVA, PVMK, PAA, PMA, PMMA, and PGMA) were measured and simulated with the DMol ab initio molecular orbital program. We performed the calculations with model compounds such as trimers, pentamers, or hexamers of the polymers. The theoretical spectra of the oligomers show a good accordance with the experimental data. With the analysis of the calculated partial densities of states it is possible to assign the spectral features to specific atomic groups of the polymers. This gives a new detailed insight into the XPS valence band structure of the investigated polymers. The presented method could also be useful to obtain informations about the chemical structure of polymers with an unknown structure from the XPS valence band spectra. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 95–103, 1999     

Theoretical study of metal‐free organic dyes based on different configurations for efficient dye‐sensitized solar cells

Considering different solar dyes configuration, four novel metal‐free organic dyes based on phenoxazine as electron donor, thiophene and cyanovinylene linkers as the ‐conjugation bridge and cyanoacrylic acid as electron acceptor were designed to optimize open circuit voltage and short circuit current parameters and theoretically inspected. Density functional theory and time‐dependent density functional theory calculations were used to study frontier molecular orbital energy states of the dyes and their optical absorption spectra. The results indicated that D2‐4 dyes can be suitable candidates as sensitizers for application in dye sensitized solar cells and among these three dyes, D3 showed a broader and more bathochromically shifted absorption band compared to the others. The dye also showed the highest molar extinction coefficient. This work suggests optimizing the configuration of metal‐free organic dyes based on simple D‐ ‐A configuration containing alkyl chain as substitution, starburst conformation, and symmetric double D‐ ‐A chains would produce good photovoltaic properties.     

Efficient blue‐emitting Ir(III) complexes with phenyl‐methyl‐benzimidazolyl and picolinate ligands: A DFT and time‐dependent DFT study

The series of heteroleptic cyclometalated Ir(III) complexes for organic light‐emitting display application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, electronic structures, and the lowest‐lying singlet absorptions and triplet emissions of Ir‐(pmb)₃ and theoretically designed models Ir‐(Rpmb)₂pic were investigated with density functional theory (DFT)‐based approaches, where pmb = phenyl‐methyl‐benzimidazolyl, pic = picolinate, and R = H/F. Their structures in the ground and excited states have been optimized at the DFT/B3LYP/LANL2DZ and TDDFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. The mobility of holes and electrons were studied computationally based on the Marcus theory. Calculations of ionization potentials were used to evaluate the injection abilities of holes into these complexes. The reasons for the higher electroluminescence efficiency and phosphorescence quantum yields in Ir‐(Rpmb)₂pic than in Ir‐(pmb)₃ have been investigated. The designed moleculars are expected to be highly emissive in pure‐blue region. © 2013 Wiley Periodicals, Inc.     

Effective potential energy curves of H2 molecule evolving in a strong time‐dependent magnetic field

Evolution of hydrogen molecule, starting initially from its field‐free ground state, in a time‐dependent (TD) magnetic field of order 10¹¹ G is presented in a parallel internuclear axis and magnetic field‐axis configuration. Effective potential energy curves (EPECs), in terms of exchange and correlation energy, of the hydrogen molecule as a function of TD magnetic‐field strength, are analyzed through TD density functional computations based on a quantum fluid dynamics approach. The numerical computations are performed for internuclear separation R ranging from 0.1 to 14.0 a.u. The EPECs exhibit field‐dependent significant potential‐well minima both at large internuclear separations and at short internuclear separations with a considerable increase in the exchange and correlation energy of the hydrogen molecule. The results, when compared with the time‐independent (TI) studies involving static TI magnetic fields, reveal TD behavior of field‐dependent crossovers between different spin‐states of hydrogen molecule as indicated by the TI investigations in static magnetic fields. Besides this, present work reveals interesting dynamics in the TD total‐electronic charge‐density distribution of the hydrogen molecule. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

ERKALE—A flexible program package for X‐ray properties of atoms and molecules

ERKALE is a novel software program for computing X‐ray properties, such as ground‐state electron momentum densities, Compton profiles, and core and valence electron excitation spectra of atoms and molecules. The program operates at Hartree–Fock or density‐functional level of theory and supports Gaussian basis sets of arbitrary angular momentum and a wide variety of exchange‐correlation functionals. ERKALE includes modern convergence accelerators such as Broyden and ADIIS and it is suitable for general use, as calculations with thousands of basis functions can routinely be performed on desktop computers. Furthermore, ERKALE is written in an object oriented manner, making the code easy to understand and to extend to new properties while being ideal also for teaching purposes. © 2012 Wiley Periodicals, Inc.     

Interaction between RNA segment (adenine‐uracil) and model of protein unit (formamide): A density‐functional theory study

Various possible structures of adenine‐uracil‐formamide hydrogen‐bond complexes were optimized at 6‐311++G(d,p) level, and the binding energies of these complexes were also calculated at DFT B3LYP/6‐311++G(d,p) level. Eight stable cyclic structures being involved in the interaction are found on the potential energy surface. By analyzing the structure, NPA charge and interaction energy of complexes, we obtain the most stable geometry structure. The results show that the interactions between formamide and adenine‐uracil (A‐U) base pair affect the stabilities of the base pairs. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Nonsingular constraints in time‐dependent variational principle for parametrized wave functions

In this work, we consider two conditions required for the nonsingularity of constraints in the time‐dependent variational principle (TDVP) for parametrized wave functions. One is the regularity condition which assures the static nonsingularity of the constraint surface. The other condition is the second‐class condition of constraints which assures the dynamic nonsingularity of the constraint surface with a symplectic metric. For analytic wave functions for complex TDVP‐parameters, the regularity and the second‐class conditions become equivalent. The second‐class condition for expectation values is reduced to the noncommutability of the corresponding quantum operators. The symplectic singularity of the equation of motion of TDVP is also shown to be a local breakdown of the second‐class condition in an extended canonical phase‐space. © 2012 Wiley Periodicals, Inc.