In this paper, we demonstrate that the optical properties of finite-sized graphene quantum dots c... more In this paper, we demonstrate that the optical properties of finite-sized graphene quantum dots can be effectively controlled by doping it with different types of charge carriers (electron/hole). In addition, the role played by a suitably directed external electric field on the optical absorption of charge-doped graphene quantum dots have also been elucidated. The computations have been performed on diamond-shaped graphene quantum dot (DQD) within the framework of the Pariser-Parr-Pople (PPP) model Hamiltonian, which takes into account long-range Coulomb interactions. Our results reveal that the energy band-gap increases when the DQD is doped with holes while it decreases on doping it with electrons. Further, the optical absorption spectra of DQD exhibits red/blue-shift on doping with electrons/holes. Our computations also indicate that the application of external transverse electric field results in a substantial blue-shift of the optical spectrum for charge-doped DQD. However, it is observed that the influence of charge-doping is more prominent in tuning the optical properties of finite-sized graphene quantum dots as compared to externally applied electric field. Thus, tailoring the optical properties of finite-sized graphene quantum dots by manipulative doping with charge carriers and suitably aligned external electric field can greatly enhance its potential application in designing nano-photonic devices.
Journal of Physics: Condensed Matter, Feb 21, 2012
Inelastic neutron scattering measurements were carried out to determine the phonon density of sta... more Inelastic neutron scattering measurements were carried out to determine the phonon density of states of ZnSe and interpreted with lattice dynamical computations (ab initio as well as a potential model). Calculations are also reported for other II-VI compounds, ZnTe and ZnS. Vibrational (phonon spectra and Grüneisen parameters), and thermal (negative thermal expansion and non-Debye specific heat) properties have been calculated and found to be in good agreement with available experimental data. This model has been further employed to study the pressure-induced solid-solid phase transitions exhibited by these compounds and the results have been compared with experimental data. Total energy calculations for zincblende and SC16 phases of ZnSe were carried out employing the pseudopotential approach under the local density approximation (LDA) as well as the generalized gradient approximation (GGA). The density functional perturbation theory is applied to study the vibrational properties of the zincblende and SC16 phases of ZnSe. An investigation of the pressure dependence of the phonon frequencies shows that the existence of the (experimentally undetected) SC16 phase as a thermodynamically stable high pressure phase is impeded due to dynamical instabilities. A detailed investigation of the polarization of phonons of different energies for the various phases of these compounds indicates that in the case of the zincblende phase the low energy modes are librational, while in the rocksalt phase the low energy modes are bending modes. Further, in ZnTe the low energy bending modes display a larger amplitude of bending than that in ZnSe and ZnS.
Employing the Pariser-Parr-Pople model Hamiltonian, we predict theoretically that the ferromagnet... more Employing the Pariser-Parr-Pople model Hamiltonian, we predict theoretically that the ferromagnetic ground state of graphene nano-fragments can undergo phase transition to a non-magnetic state on the application of an external electric field. Our results indicate that the energy gaps for up and down spins are degenerate in the absence of electric field. However, this degeneracy is lifted under the influence of an external electric field. This selective tuning of the different magnetic states as well as their energy gaps in graphene nano-fragments by an externally applied electric field can be efficiently exploited in designing nano-scale spin polarized field effect transistors. Keywords—graphene nano-fragments; electric field; phase transition. __________________________________________________*****_________________________________________________
This work demonstrates the unique approach of introducing divacancy imperfections in topological ... more This work demonstrates the unique approach of introducing divacancy imperfections in topological Stone-Wales type defected graphene quantum dots for harvesting both singlet and triplet excitons, essential for fabricating fluorescent organic light-emitting diodes. Here, we first reveal that structural relaxation of these systems establishes the high-spin triplet state as the stable ground state at room temperature, thereby significantly increasing their potential in designing spintronic devices. Our extensive electron-correlated computations then demonstrate that the energetic ordering of the singlet and triplet states in these relaxed structures can trigger both prompt and delayed 1
In this work, we report for the first time the crucial role of topological anomalies like Stone-W... more In this work, we report for the first time the crucial role of topological anomalies like Stone-Wales (SW) type bond rotations in tuning the optical properties of graphene quantum dots (GQDs). By means of first-principles calculations, we first show that the structural stability of GQDs strongly depends on position of SW defects. Optical absorption spectra is then computed using electron-correlated methodology to demonstrate that SW type reconstruction is responsible for the appearance of new defect-induced peaks below the optical gap and dramatically modifies the optical absorption profile. In addition, our investigations signify that electron correlation effects become more dominant for SW-defected GQDs. We finally establish that the introduction of SW defects at specific locations strongly enhances light absorption in visible range, which is of prime importance for designing light harvesting, photocatalytic and optoelectronic devices.
In quasi-1D π-conjugated polymers such as trans-polyacetylene and polyenes, electron correlation ... more In quasi-1D π-conjugated polymers such as trans-polyacetylene and polyenes, electron correlation effects determine the "reversed" excited state ordering in which the lowest two-photon 2A g state lies below the lowest one-photon 1B u state. In this work, we present conclusive theoretical evidence of reversed excited state ordering in fairly 2D π-conjugated systems, namely, diamond-shaped graphene quantum dots (DQDs). Our electron correlated calculations show that DQDs begin to exhibit reversed excited ordering with increasing size, in disagreement with independent-particle picture. This signals the onset of strong correlation effects which renders them nonluminescent. Further, we calculate and analyze the two-photon absorption (TPA) spectra as well as photoinduced absorption (PA) spectra of these systems and find excellent agreement with the available experimental results. Our investigations demonstrate that unlike a strictly 1D system like transpolyacetylene, the non-linear and excited state absorptions in DQDs are highly intricate, with several even parity states responsible for strong absorptions. Our results could play an important role in the design of graphene-based non-linear optical devices.
In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) h... more In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the pi-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects. Furthermore, an analysis of the wave functions of the excited states contributing to the spectra reveals the presence of plasmonic effects.
In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) h... more In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the π-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electroncorrelation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects. Furthermore, an analysis of the wave functions of the excited states contributing to the spectra reveals the presence of plasmonic effects. 1 arXiv:1501.06041v1 [cond-mat.mes-hall] 24 Jan 2015 Because of aforesaid possibilities of applications of GQDs, significant studies, experimental, as well as theoretical, on the electronic and optical properties of GQDs have been performed lately. Experimental studies on GQDs (in the size range of 5-35 nm) by Kim et al. 7 have revealed that while the absorption peak energies decrease with increasing size of the GQDs, the photoluminescence (PL) spectra exhibit a decrease in energy as the average size of GQDs increases up to ∼17 nm, followed by an increase in the peak energy with increasing average size of GQDs. They accredited this abnormal behavior of PL spectra to the presence of edge variations associated with size-dependent shape in GQDs. However, single-particle spectroscopic measurements carried out by Xu et al. 10 have shown that size differences of GQDs do not affect the peak positions and spectral line-shapes. Experiments the UV-Vis absorption spectrum of Dibenzo[bc,kl]coronene posted at http://pah.nist.gov/?q=pah376 .
In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) h... more In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the $\pi$-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron-correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlat...
ABSTRACT Inelastic neutron scattering measurements to determine the phonon density of states alon... more ABSTRACT Inelastic neutron scattering measurements to determine the phonon density of states along with lattice dynamical studies based on a supercell and a simple transferable potential model have been done to confirm the two mode behavior exhibited by ZnS1-xSex. In addition, the contribution of bond-length distribution to the existence of anomalous modes found in the frequency range of the ZnS-like TO and LO modes has been emphasized.
CITATIONS 0 READS 34 12 authors, including: Some of the authors of this publication are also work... more CITATIONS 0 READS 34 12 authors, including: Some of the authors of this publication are also working on these related projects: Atomic modeling of the properties of the materials for photovotaic applications View project A. Ivanov Institut Laue-Langevin 193 PUBLICATIONS 3,928 CITATIONS
ABSTRACT In this paper, we put forth a microscopic interpretation of the characteristics of vibra... more ABSTRACT In this paper, we put forth a microscopic interpretation of the characteristics of vibrational spectra of zinc blende semiconductor alloys arising due to either difference in masses or contrast in bond lengths. Previous Raman and infrared experiments have helped in identifying two mode vibrational behaviors in mixed systems of Zn1−xMgxSe and Zn1−xMgxTe in contrast to the one-mode behavior in Zn1−xMgxS. Our lattice dynamics computations have elucidated that in addition to the mass of the anion, bond length anomalies, energy separation between the two sets of optical modes, and the magnitudes of the scattering cross section play an important role in the observance of one mode behavior in the S system, two mode behavior for the whole of the composition range in the Se and Te systems, and an additional Be–Te like vibrational doublet in case of Zn1−xBexTe. Our calculations incorporate the treatment of disorder through a supercell approach. The calculated lattice constants for different concentrations, the bimodal bond length distribution, as well as the phonon frequencies at the Brillouin zone centre are in good agreement with the available experimental data.
A transferable shell model potential has been employed to study the pressure-induced solid-solid ... more A transferable shell model potential has been employed to study the pressure-induced solid-solid phase transitions exhibited by BeSe and BeTe. A detailed investigation of the Gibbs free energy has revealed the relative stability of the different phases for BeSe and BeTe. In addition, a microscopic analysis of the polarization of phonons of different energies for the various phases indicate the
ABSTRACT Lattice dynamical calculations of ZnGeP2 and ZnSnP2 have been performed to investigate t... more ABSTRACT Lattice dynamical calculations of ZnGeP2 and ZnSnP2 have been performed to investigate the possibility of the existence of the ordered chalcopyrite-to-disordered zincblende phase transition exhibited by some similar compounds and to understand the role played by phonons. The calculated values of the lattice parameters, bulk modulii and vibrational frequencies are in good agreement with the available experimental data. We observe that with increase in pressure the transverse acoustic branches and the lowest lying optic mode show a softening, which is eventually followed by elastic instability (at 3 GPa and 6.5 GPa respectively for ZnGeP2 and ZnSnP2) of the chalcopyrite phase. However, the disordered cubic phase is found to be dynamically and mechanically stable at these pressures.
In this paper, we demonstrate that the optical properties of finite-sized graphene quantum dots c... more In this paper, we demonstrate that the optical properties of finite-sized graphene quantum dots can be effectively controlled by doping it with different types of charge carriers (electron/hole). In addition, the role played by a suitably directed external electric field on the optical absorption of charge-doped graphene quantum dots have also been elucidated. The computations have been performed on diamond-shaped graphene quantum dot (DQD) within the framework of the Pariser-Parr-Pople (PPP) model Hamiltonian, which takes into account long-range Coulomb interactions. Our results reveal that the energy band-gap increases when the DQD is doped with holes while it decreases on doping it with electrons. Further, the optical absorption spectra of DQD exhibits red/blue-shift on doping with electrons/holes. Our computations also indicate that the application of external transverse electric field results in a substantial blue-shift of the optical spectrum for charge-doped DQD. However, it is observed that the influence of charge-doping is more prominent in tuning the optical properties of finite-sized graphene quantum dots as compared to externally applied electric field. Thus, tailoring the optical properties of finite-sized graphene quantum dots by manipulative doping with charge carriers and suitably aligned external electric field can greatly enhance its potential application in designing nano-photonic devices.
Journal of Physics: Condensed Matter, Feb 21, 2012
Inelastic neutron scattering measurements were carried out to determine the phonon density of sta... more Inelastic neutron scattering measurements were carried out to determine the phonon density of states of ZnSe and interpreted with lattice dynamical computations (ab initio as well as a potential model). Calculations are also reported for other II-VI compounds, ZnTe and ZnS. Vibrational (phonon spectra and Grüneisen parameters), and thermal (negative thermal expansion and non-Debye specific heat) properties have been calculated and found to be in good agreement with available experimental data. This model has been further employed to study the pressure-induced solid-solid phase transitions exhibited by these compounds and the results have been compared with experimental data. Total energy calculations for zincblende and SC16 phases of ZnSe were carried out employing the pseudopotential approach under the local density approximation (LDA) as well as the generalized gradient approximation (GGA). The density functional perturbation theory is applied to study the vibrational properties of the zincblende and SC16 phases of ZnSe. An investigation of the pressure dependence of the phonon frequencies shows that the existence of the (experimentally undetected) SC16 phase as a thermodynamically stable high pressure phase is impeded due to dynamical instabilities. A detailed investigation of the polarization of phonons of different energies for the various phases of these compounds indicates that in the case of the zincblende phase the low energy modes are librational, while in the rocksalt phase the low energy modes are bending modes. Further, in ZnTe the low energy bending modes display a larger amplitude of bending than that in ZnSe and ZnS.
Employing the Pariser-Parr-Pople model Hamiltonian, we predict theoretically that the ferromagnet... more Employing the Pariser-Parr-Pople model Hamiltonian, we predict theoretically that the ferromagnetic ground state of graphene nano-fragments can undergo phase transition to a non-magnetic state on the application of an external electric field. Our results indicate that the energy gaps for up and down spins are degenerate in the absence of electric field. However, this degeneracy is lifted under the influence of an external electric field. This selective tuning of the different magnetic states as well as their energy gaps in graphene nano-fragments by an externally applied electric field can be efficiently exploited in designing nano-scale spin polarized field effect transistors. Keywords—graphene nano-fragments; electric field; phase transition. __________________________________________________*****_________________________________________________
This work demonstrates the unique approach of introducing divacancy imperfections in topological ... more This work demonstrates the unique approach of introducing divacancy imperfections in topological Stone-Wales type defected graphene quantum dots for harvesting both singlet and triplet excitons, essential for fabricating fluorescent organic light-emitting diodes. Here, we first reveal that structural relaxation of these systems establishes the high-spin triplet state as the stable ground state at room temperature, thereby significantly increasing their potential in designing spintronic devices. Our extensive electron-correlated computations then demonstrate that the energetic ordering of the singlet and triplet states in these relaxed structures can trigger both prompt and delayed 1
In this work, we report for the first time the crucial role of topological anomalies like Stone-W... more In this work, we report for the first time the crucial role of topological anomalies like Stone-Wales (SW) type bond rotations in tuning the optical properties of graphene quantum dots (GQDs). By means of first-principles calculations, we first show that the structural stability of GQDs strongly depends on position of SW defects. Optical absorption spectra is then computed using electron-correlated methodology to demonstrate that SW type reconstruction is responsible for the appearance of new defect-induced peaks below the optical gap and dramatically modifies the optical absorption profile. In addition, our investigations signify that electron correlation effects become more dominant for SW-defected GQDs. We finally establish that the introduction of SW defects at specific locations strongly enhances light absorption in visible range, which is of prime importance for designing light harvesting, photocatalytic and optoelectronic devices.
In quasi-1D π-conjugated polymers such as trans-polyacetylene and polyenes, electron correlation ... more In quasi-1D π-conjugated polymers such as trans-polyacetylene and polyenes, electron correlation effects determine the "reversed" excited state ordering in which the lowest two-photon 2A g state lies below the lowest one-photon 1B u state. In this work, we present conclusive theoretical evidence of reversed excited state ordering in fairly 2D π-conjugated systems, namely, diamond-shaped graphene quantum dots (DQDs). Our electron correlated calculations show that DQDs begin to exhibit reversed excited ordering with increasing size, in disagreement with independent-particle picture. This signals the onset of strong correlation effects which renders them nonluminescent. Further, we calculate and analyze the two-photon absorption (TPA) spectra as well as photoinduced absorption (PA) spectra of these systems and find excellent agreement with the available experimental results. Our investigations demonstrate that unlike a strictly 1D system like transpolyacetylene, the non-linear and excited state absorptions in DQDs are highly intricate, with several even parity states responsible for strong absorptions. Our results could play an important role in the design of graphene-based non-linear optical devices.
In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) h... more In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the pi-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects. Furthermore, an analysis of the wave functions of the excited states contributing to the spectra reveals the presence of plasmonic effects.
In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) h... more In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the π-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electroncorrelation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects. Furthermore, an analysis of the wave functions of the excited states contributing to the spectra reveals the presence of plasmonic effects. 1 arXiv:1501.06041v1 [cond-mat.mes-hall] 24 Jan 2015 Because of aforesaid possibilities of applications of GQDs, significant studies, experimental, as well as theoretical, on the electronic and optical properties of GQDs have been performed lately. Experimental studies on GQDs (in the size range of 5-35 nm) by Kim et al. 7 have revealed that while the absorption peak energies decrease with increasing size of the GQDs, the photoluminescence (PL) spectra exhibit a decrease in energy as the average size of GQDs increases up to ∼17 nm, followed by an increase in the peak energy with increasing average size of GQDs. They accredited this abnormal behavior of PL spectra to the presence of edge variations associated with size-dependent shape in GQDs. However, single-particle spectroscopic measurements carried out by Xu et al. 10 have shown that size differences of GQDs do not affect the peak positions and spectral line-shapes. Experiments the UV-Vis absorption spectrum of Dibenzo[bc,kl]coronene posted at http://pah.nist.gov/?q=pah376 .
In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) h... more In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the $\pi$-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron-correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlat...
ABSTRACT Inelastic neutron scattering measurements to determine the phonon density of states alon... more ABSTRACT Inelastic neutron scattering measurements to determine the phonon density of states along with lattice dynamical studies based on a supercell and a simple transferable potential model have been done to confirm the two mode behavior exhibited by ZnS1-xSex. In addition, the contribution of bond-length distribution to the existence of anomalous modes found in the frequency range of the ZnS-like TO and LO modes has been emphasized.
CITATIONS 0 READS 34 12 authors, including: Some of the authors of this publication are also work... more CITATIONS 0 READS 34 12 authors, including: Some of the authors of this publication are also working on these related projects: Atomic modeling of the properties of the materials for photovotaic applications View project A. Ivanov Institut Laue-Langevin 193 PUBLICATIONS 3,928 CITATIONS
ABSTRACT In this paper, we put forth a microscopic interpretation of the characteristics of vibra... more ABSTRACT In this paper, we put forth a microscopic interpretation of the characteristics of vibrational spectra of zinc blende semiconductor alloys arising due to either difference in masses or contrast in bond lengths. Previous Raman and infrared experiments have helped in identifying two mode vibrational behaviors in mixed systems of Zn1−xMgxSe and Zn1−xMgxTe in contrast to the one-mode behavior in Zn1−xMgxS. Our lattice dynamics computations have elucidated that in addition to the mass of the anion, bond length anomalies, energy separation between the two sets of optical modes, and the magnitudes of the scattering cross section play an important role in the observance of one mode behavior in the S system, two mode behavior for the whole of the composition range in the Se and Te systems, and an additional Be–Te like vibrational doublet in case of Zn1−xBexTe. Our calculations incorporate the treatment of disorder through a supercell approach. The calculated lattice constants for different concentrations, the bimodal bond length distribution, as well as the phonon frequencies at the Brillouin zone centre are in good agreement with the available experimental data.
A transferable shell model potential has been employed to study the pressure-induced solid-solid ... more A transferable shell model potential has been employed to study the pressure-induced solid-solid phase transitions exhibited by BeSe and BeTe. A detailed investigation of the Gibbs free energy has revealed the relative stability of the different phases for BeSe and BeTe. In addition, a microscopic analysis of the polarization of phonons of different energies for the various phases indicate the
ABSTRACT Lattice dynamical calculations of ZnGeP2 and ZnSnP2 have been performed to investigate t... more ABSTRACT Lattice dynamical calculations of ZnGeP2 and ZnSnP2 have been performed to investigate the possibility of the existence of the ordered chalcopyrite-to-disordered zincblende phase transition exhibited by some similar compounds and to understand the role played by phonons. The calculated values of the lattice parameters, bulk modulii and vibrational frequencies are in good agreement with the available experimental data. We observe that with increase in pressure the transverse acoustic branches and the lowest lying optic mode show a softening, which is eventually followed by elastic instability (at 3 GPa and 6.5 GPa respectively for ZnGeP2 and ZnSnP2) of the chalcopyrite phase. However, the disordered cubic phase is found to be dynamically and mechanically stable at these pressures.
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computations have been performed using the pi-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects. Furthermore, an analysis of the wave functions of the excited states contributing to the spectra reveals the presence of plasmonic effects.
computations have been performed using the pi-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects. Furthermore, an analysis of the wave functions of the excited states contributing to the spectra reveals the presence of plasmonic effects.