Quantum computation: From Church-Turing thesis to Qubits

Kundu, Shankhadip; Kundu, Rajdeep; Kundu, Shubhabrata; Bhattachaijee, Anubhab; Gupta, Sayantan; Ghosh, Souvik; Basu, Indranil

doi:10.1109/uemcon.2016.7777805

Cited by 8 publications

(2 citation statements)

References 12 publications

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“…For the frozen phonon and stochastic calculations, we used the PyEPFD package 35 to generate displaced structures and Qbox for DFT calculations. Specifically, the Qbox outputs were post-processed with the PyEPFD package to compute the dynamical matrix, phonon frequencies, phonon eigenvectors, and renormalized energy gaps.…”

Section: Methodsmentioning

confidence: 99%

Quantum Vibronic Effects on the Electronic Properties of Molecular Crystals

Kundu

Galli

2023

J. Chem. Theory Comput.

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We present a study of molecular crystals, focused on the effect of nuclear quantum motion and anharmonicity on their electronic properties. We consider a system composed of relatively rigid molecules, a diamondoid crystal, and one composed of floppier molecules, NAI-DMAC, a thermally activated delayed fluorescence compound. We compute fundamental electronic gaps at the density functional theory (DFT) level of theory, with the Perdew−Burke−Erzenhof (PBE) and strongly constrained and approximately normed (SCAN) functionals, by coupling firstprinciples molecular dynamics with a nuclear quantum thermostat. We find a sizable zero-point renormalization (ZPR) of the band gaps, which is much larger in the case of diamondoids (0.6 eV) than for NAI-DMAC (0.22 eV). We show that the frozen phonon (FP) approximation, which neglects intermolecular anharmonic effects, leads to a large error (∼50%) in the calculation of the band gap ZPR. Instead, when using a stochastic method, we obtain results in good agreement with those of our quantum simulations for the diamondoid crystal. However, the agreement is worse for NAI-DMAC where intramolecular anharmonicities contribute to the ZPR. Our results highlight the importance of accurately including nuclear and anharmonic quantum effects to predict the electronic properties of molecular crystals.

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Section: Methodsmentioning

confidence: 99%

Quantum Vibronic Effects on the Electronic Properties of Molecular Crystals

Kundu

Galli

2023

J. Chem. Theory Comput.

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“…FPMD simulations were carried out using the i-PI–Qbox coupling scheme, , where the i-PI package moves the nuclei and the Qbox code provides forces on the nuclei by solving the Kohn–Sham equations. For the stochastic simulations, we generated 200 independent displaced configurations and their antithetic pairs (resulting in 400 configurations) using the PyEPFD package ,, and performed DFT single-point calculations using the Qbox code (see section S3 for further computational details).…”

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confidence: 99%

Quantum Vibronic Effects on the Excitation Energies of the Nitrogen-Vacancy Center in Diamond

Kundu,

Galli

2024

J. Phys. Chem. Lett.

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We investigated the impact of quantum vibronic coupling on the electronic properties of solid-state spin defects using stochastic methods and first-principles molecular dynamics with a quantum thermostat. Focusing on the negatively charged nitrogen-vacancy center in diamond as an exemplary case, we found a significant dynamic Jahn–Teller splitting of the doubly degenerate single-particle levels within the diamond’s band gap, even at 0 K, with a magnitude exceeding 180 meV. This pronounced splitting leads to substantial renormalizations of these levels and, subsequently, of the vertical excitation energies of the doubly degenerate singlet and triplet excited states. Our findings underscore the pressing need to incorporate quantum vibronic effects into first-principles calculations, particularly when comparing computed vertical excitation energies with experimental data. Our study also reveals the efficiency of stochastic thermal line sampling for studying phonon renormalizations of solid-state spin defects.

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Limitations and Usefulness of Computer Simulations for Complex Adaptive Systems Research

Tolk¹

2019

Simulation Foundations, Methods and Applications

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Quantum computation: From Church-Turing thesis to Qubits

Cited by 8 publications

References 12 publications

Quantum Vibronic Effects on the Electronic Properties of Molecular Crystals

Quantum Vibronic Effects on the Electronic Properties of Molecular Crystals

Quantum Vibronic Effects on the Excitation Energies of the Nitrogen-Vacancy Center in Diamond

Limitations and Usefulness of Computer Simulations for Complex Adaptive Systems Research

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