Electronic structure, lattice energies and Born exponents for alkali halides from first principles

Gopikrishnan, C. R.; Jose, Deepthi; Datta, Ayan

doi:10.1063/1.3684608

Cited by 49 publications

(26 citation statements)

References 32 publications

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“…We note that in all cases, the minimum energy gap is direct at the Γ point as found from the EV approximation; whereas earlier DFT calculations exhibit the well‐known severe underestimation of energy gaps. Furthermore the qualitative features in these band structures are found to be very similar.…”

Section: Resultssupporting

confidence: 47%

“…However the density functional theory (DFT) [2] calculations within the local density approximation (LDA) [3] or generalized gradient approximation (GGA) [4] give rise to a typical underestimation of electronic excitation energies, such as energy gaps. For instance, the calculated [5][6] lowest band gaps are severely underestimated compared to experiment. This is the case of calculated LDA band gaps [5] of 7.26, 6.38, 5.84, and 4.37 eV for NaF, NaCl, NaBr, and NaI, respectively, compared to the measured values [7] of 11.5, 8.75, 7.1, and 5.9 eV.…”

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confidence: 89%

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Band‐gap and phonon distribution in alkali halides

Messaoudi

Zaoui

Ferhat

2014

Physica Status Solidi (b)

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A systematic first‐principles study is performed to calculate the structural, electronic, dynamical, and thermodynamic properties of alkali halides NaF, NaCl, NaBr, and NaI by means of both full‐potential linear augmented plane‐wave, and plane wave pseudopotential methods. The obtained structural parameters agree favourably with experimental findings. The calculated band gaps are underestimated by GGA functional compared to experiment. The gap values are improved from the modified Becke–Johnson exchange potential, which gives band gaps in perfect agreement with the measured values. In addition, linear‐response approach to the density functional theory is used to derive several quantities such as the Born effective charges, high‐frequency dielectric constant, phonon band structure, and phonon density of states. The dynamical properties of Na‐based alkali halides are also analysed and discussed. Finally the temperature dependence of various quantities such as the mean‐squared displacement, and the heat capacity are computed using the quasi‐harmonic approximation.

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Section: Resultssupporting

confidence: 47%

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confidence: 89%

Band‐gap and phonon distribution in alkali halides

Messaoudi

Zaoui

Ferhat

2014

Physica Status Solidi (b)

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“…The PBE energy gap computed using the polarisation-optimised basis set 3 (9.15 eV) is in good agreement with recent calculations based on the projector augmented wave (PAW) approach (8.94 eV) 62 . We find the B3LYP energy gap to be at least 2 eV smaller than the band gap, which is unusual, considering the well known ability of B3LYP to approximate, typically very accurately, band gaps of semiconductors and some classes of wide-gap insulators, e.g.…”

Section: 45supporting

confidence: 73%

Optical properties of alkali halide crystals from all-electron hybrid TD-DFT calculations

Webster

Bernasconi

Harrison

2015

The Journal of Chemical Physics

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We present a study of the electronic and optical properties of a series of alkali halide crystals AX, with A=Li, Na, K, Rb and X=F, Cl, Br based on a recent implementation of hybrid-exchange TD-DFT (TD-B3LYP) in the all-electron Gaussian basis set code CRYSTAL. We examine, in particular, the impact of basis set size and quality on the prediction of the optical gap and exciton binding energy.The formation of bound excitons by photoexcitation is observed in all the studied systems and this is shown to be correlated to specific features of the Hartree-Fock exchange component of the TD-DFT response kernel. All computed optical gaps and exciton binding energies are however markedly below estimated experimental and, where available, 2-particle Green's function (GW-BSE) values. We attribute this reduced exciton binding to the incorrect asymptotics of the B3LYP exchange correlation ground state functional and of the TD-B3LYP response kernel, which lead to a large underestimation of the Coulomb interaction between the excited electron and hole wavefunctions. Considering LiF as an example, we correlate the asymptotic behaviour of the TD-B3LYP kernel to the fraction of Fock exchange admixed in the ground state functional c HF , and show that there exists one value of c HF (∼0.32) that reproduces at least semi-quantitatively the optical gap of this material.

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“…Besides melting points, other properties were evaluated for alkali halides using first principle calculations. Gopikrishnan et al 20 calculated lattice energies of alkali halides with an RMSD of E70 kJ mol À1 that, in fact, can be predicted more accurately by our polarizable model using classical MD simulations (RMSD 16 kJ mol À1 ) and other force fields. 6 On the other hand, first principle calculations offer the possibility to calculate properties such as the band-structures of materials that cannot be obtained with classical simulations.…”

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confidence: 80%

“…6 On the other hand, first principle calculations offer the possibility to calculate properties such as the band-structures of materials that cannot be obtained with classical simulations. 20 However, quantum chemistry methods remain severely limited by computational demands and nanosecond simulations for systems of thousands of particles are still firmly out of reach for first principles MD simulations. Therefore, accurate classical MD simulations remain the most practical route to study properties such as melting points of complex systems.…”

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confidence: 99%