Relationship between orbital energy gaps and excitation energies for long-chain systems

2016 ◽  
Vol 37 (16) ◽  
pp. 1451-1462 ◽  
Author(s):  
Takao Tsuneda ◽  
Raman K. Singh ◽  
Ayako Nakata
Keyword(s):  
Orbital Energy ◽  
Excitation Energies ◽  
Energy Gaps ◽  
Long Chain

Orbital-based Descriptions of Electron Configurations, Ionization, Excitation, and Bonding

2020 ◽  
pp. 188-216
Author(s):  
Jochen Autschbach
Keyword(s):  
Molecular Orbital ◽  
Ground State ◽  
Orbital Energy ◽  
Chemical Bonds ◽  
Theory Construction ◽  
Electronic Excitations ◽  
Energy Gaps ◽  
Koopmans Theorem ◽  
Total Energies ◽  
Ground State Electron

This chapter deals with quantitative aspects of molecular orbital (MO) theory: Construction of an orbital diagram, bonding and antibonding overlap, Koopmans’ theorem, orbital energies versus total energies, an explanation of the unintuitive ground state electron configurations seen for some neutral transition metals, and a discussion of orbital energy gaps versus electronic excitations and other observable energy gaps. Localized MOs show the chemical bonds expected from the Lewis structure more readily than the canonical orbitals obtained from solving the SCF equations. It is shown that the delocalization of localized, not the canonical, MOs shows whether a system is delocalized. Algorithms by which to obtain localized MOs are sketched.

Photoluminescence in Hydrogenated Amorphous Silicon with Sulfur

1996 ◽  
Vol 420 ◽  
Author(s):  
S. Chen ◽  
P. C. Taylor ◽  
S. L. Wang ◽  
J. M. Viner
Keyword(s):  
Sulfur Concentration ◽  
Absorption Coefficients ◽  
Excitation Energies ◽  
Phosphorus Doping ◽  
Pl Spectra ◽  
Sulfur Doping ◽  
Photothermal Deflection Spectroscopy ◽  
Energy Gaps ◽  
Phosphorus Doped ◽  
Hydrogenated Amorphous

AbstractPhotoluminescence (PL) has been measured at 80 K in a series of samples of sulfur doped a- Si:H using above- and below-bandgap excitation energies (2.4 and 1.38 eV). In addition, the absorption coefficients at room temperature have been obtained using photothermal deflection spectroscopy (PDS). At light sulfur doping levels (S/Si < 10-2), the Urbach slopes of the absorption coefficients on a semilog plot and the optical energy gaps, as measured by the points at which ca =104 cm-1, are independent of sulfur concentration. The slopes decrease and optical gaps increase with increasing doping level for doping levels above 10-2. At light sulfur doping levels the PL spectra excited with both above- and below-gap light are independent of sulfur concentration. For larger sulfur concentrations the shapes of the PL spectra vary. In particular, for S/Si > 10-2the peak of the PL spectrum shifts to below 0.8 eV using below-gap excitation at 1.38 eV, and the defect PL band dominates. Comparing the PL spectra of sulfur- and phosphorus-doped samples, the PL spectra change for sulfur doping above 10-2 and for phosphorus doping above 1 ppm. This trend is consistent with inefficient sulfur doping.

scholarly journals Fewest switches surface hopping with Baeck-An couplings

2021 ◽  
Vol 1 ◽  
pp. 49
Author(s):  
Mariana T. do Casal ◽  
Josene M. Toldo ◽  
Max Pinheiro Jr ◽  
Mario Barbatti
Keyword(s):  
Density Functional ◽  
Time Dependent ◽  
Test Results ◽  
Nonadiabatic Dynamics ◽  
Excitation Energies ◽  
Functional Theory ◽  
Surface Hopping ◽  
Energy Gaps ◽  
Potential Use ◽  
Adiabatic Energy

In the Baeck-An (BA) approximation, first-order nonadiabatic coupling vectors are given in terms of adiabatic energy gaps and the second derivative of the gaps with respect to the coupling coordinate. In this paper, a time-dependent (TD) BA approximation is derived, where the couplings are computed from the energy gaps and their second time-derivatives. TD-BA couplings can be directly used in fewest switches surface hopping, enabling nonadiabatic dynamics with any electronic structure methods able to provide excitation energies and energy gradients. Test results of surface hopping with TD-BA couplings for ethylene and fulvene show that the TD-BA approximation delivers a qualitatively correct picture of the dynamics and a semiquantitative agreement with reference data computed with exact couplings. Nevertheless, TD-BA does not perform well in situations conjugating strong couplings and small velocities. Considered the uncertainties in the method, TD-BA couplings could be a competitive approach for inexpensive, exploratory dynamics with a small trajectories ensemble. We also assessed the potential use of TD-BA couplings for surface hopping dynamics with time-dependent density functional theory (TDDFT), but the results are not encouraging due to singlet instabilities near the crossing seam with the ground state.

Excitation energies, singlet–triplet energy gaps, spin–orbit matrix elements and heavy atom effects in BOIMPYs as possible photosensitizers for photodynamic therapy: a computational investigation

2018 ◽  
Vol 20 (4) ◽  
pp. 2656-2661 ◽  
Author(s):  
Bruna Clara De Simone ◽  
Gloria Mazzone ◽  
Nino Russo ◽  
Emilia Sicilia ◽  
Marirosa Toscano
Keyword(s):  
Photodynamic Therapy ◽  
Photophysical Properties ◽  
Heavy Atom ◽  
Spin Orbit ◽  
Matrix Elements ◽  
Computational Investigation ◽  
Triplet Energy ◽  
Excitation Energies ◽  
Halogen Atoms ◽  
Energy Gaps

Introduction of halogen atoms in different amounts and positions into the BOIMPY skeleton significantly affects its photophysical properties.

Fermi-Amaldi model for exchange-correlation: atomic excitation energies from orbital energy differences

2005 ◽  
Vol 103 (15-16) ◽  
pp. 2061-2072 ◽  
Author(s):  
Paul W. Ayers * ◽  
Robert C. Morrison ◽  
Robert G. Parr
Keyword(s):  
Orbital Energy ◽  
Excitation Energies ◽  
Exchange Correlation ◽  
Atomic Excitation

scholarly journals 3(4)-Amino-4(3)-nitro-1,2,5-oxadiazole-2-oxides and their Ring-opened Isomers-A DFT Treatment

2020 ◽  
pp. 35-51
Author(s):  
Lemi Türker
Keyword(s):  
Molecular Orbital ◽  
Ring Opening ◽  
Density Functional ◽  
Transition States ◽  
Activation Energies ◽  
Functional Treatment ◽  
Orbital Energy ◽  
Energy Gaps ◽  
Molecular Orbital Energy ◽  
Homo Lumo

Amino and nitro substituted 1,2,5-oxadiazole-2-oxide isomers and their ring-opened nitroso forms have been subjected to density functional treatment at the level of B3LYP/6-311++G(d,p). The transition states for the ring opening processes are obtained and the corresponding activation energies have been calculated. Also, 1,3- and 1,5-proton tautomerism yielding imine, oxime and aci forms are investigated. For all the structures, the stabilities, the HOMO, LUMO energies and the interfrontier molecular orbital energy gaps are obtained and the effects of substituents (NH2 and NO2) are discussed.

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