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Your search keyword '"Silkinis, Rokas"' showing total 3 results
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3 results on '"Silkinis, Rokas"'

1. Optical lineshapes for orbital singlet to doublet transitions in a dynamical Jahn-Teller system: the NiV$^{-}$ center in diamond

Author

Silkinis, Rokas, Žalandauskas, Vytautas, Thiering, Gergő, Gali, Adam, Van de Walle, Chris G., Alkauskas, Audrius, and Razinkovas, Lukas

Subjects
Condensed Matter - Materials Science
Abstract

We apply density functional theory to investigate interactions between electronic and vibrational states in crystal defects with multi-mode dynamical Jahn-Teller (JT) systems. Our focus is on transitions between orbital singlet and degenerate orbital doublet characterized by $E \otimes (e \oplus e \oplus \cdots)$ JT coupling, which frequently occurs in crystal defects that are investigated for applications in quantum information science. We utilize a recently developed methodology to model the photoluminescence (PL) spectrum of the negatively charged split nickel-vacancy center (NiV$^{-}$) in diamond, where JT-active modes significantly influence electron-phonon interactions. Our results validate the effectiveness of the methodology in accurately reproducing the observed 1.4 eV PL lineshape. The strong agreement between our theoretical predictions and experimental observations reinforces the identification of the 1.4 eV PL center with the NiV$^{-}$ complex. This study highlights the critical role of JT-active modes in affecting optical lineshapes and demonstrates the power of advanced techniques for modeling optical properties in complex systems with multiple JT-active frequencies., Comment: 13 pages, 7 figures

Published
2024

2. The application of the SCAN density functional to color centers in diamond.

Author

Maciaszek, Marek, Žalandauskas, Vytautas, Silkinis, Rokas, Alkauskas, Audrius, and Razinkovas, Lukas

Subjects
DENSITY functionals, POTENTIAL energy surfaces, DIAMONDS, DENSITY functional theory, ELECTRONIC structure, FUNCTIONALS, JEWELRY stores, PHOTOVOLTAIC power systems
Abstract

Detailed characterization of deep-level color centers requires understanding their electronic and atomic structure, which is most commonly investigated utilizing the Kohn–Sham density functional theory. Standard semilocal functionals based on the generalized gradient approximation (GGA) are inclined toward an imprecise quantitative description of defects' electronic structure. Hybrid functionals provide an improved prediction of electronic properties, albeit at a much higher computational cost. In this work, we test the newly developed Strongly Constrained and Appropriately Normed (SCAN) family of meta-GGA density functionals for selected color centers in diamond. In particular, we study nitrogen-, silicon-, germanium-, and tin-vacancy centers that have been recently investigated for their use in quantum technological applications. We show that SCAN and its derivatives, the rSCAN and r2SCAN functionals, significantly improve the calculated energies of optical transitions within the delta-self-consistent-field approach, almost reaching the accuracy of the hybrid Heyd–Scuseria–Ernzerhof (HSE) functional. In the case of the NV− center, we also show that the SCAN family of functionals improves the description of the adiabatic potential energy surfaces compared to both GGA and hybrid functionals, improving calculated luminescence lineshapes. As a result of these findings, we recommend using the SCAN family of functionals as a promising alternative for studying color centers in solids. [ABSTRACT FROM AUTHOR]

Published
2023
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3. Electronic structure of the divacancy defect in gallium nitride

Author

Silkinis, Rokas and Alkauskas, Audrius

Abstract

Properties of materials are strongly influenced by the presence of defects and impurities. This effect is particularly strong in the case of semiconductor materials. As these materials are widely used in the production of various electronic devices (lasers, light-emitting diodes), their theoretical analysis is of utmost importance. Gallium nitride (GaN) is a particularly important semiconductor that enabled the creation of high-brightness LEDs in the blue-UV region of the spectrum. Recently, using experimental evidence, a hypothesis was put forward which states that nitrogen vacancies and gallium-nitrogen divacancies present in GaN act as non-radiative recombination centers, limiting the efficiency of radiative processes in optoelectronic devices. However, currently there is no consensus regarding the defects that cause non-radiative recombination in GaN. The main goal of this work was to analyse the electronic structure of hexagonal wurtzite crystal structure GaN having a gallium-nitrogen divacancy and either confirm or deny the hypothesis that this divacancy can act as an efficient recombination center. Density functional theory was used to perform calculations from first principles on a supercell of 126 atoms. This was done using VASP software suite. Spin-polarized calculations were performed using the HSE form of the hybrid functional. The main results of this work involve a formation energy diagram of the divacancy complex in different charge states (q = +1; 0; -1; -2) and an energy level diagram of a supercell with a neutral (q = 0) divacancy, for which an approximate excitation energy between two defect levels inside the band gap was calculated. The results indicate that the divacancy defect has similar properties to the VGa-ON complex, which was already shown to behave as an inefficient non-radiative recombination center in GaN.

Published
2020

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