Ab initio two-dimensional multiband low-energy models of EtMe 3Sb[Pd(dmit) 2] 2 and κ-(BEDT-TTF) 2Cu(NCS) 2 with comparisons to single-band models

Kazuma Nakamura, Yoshihide Yoshimoto, Masatoshi Imada

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Abstract

We present ab initio two-dimensional extended Hubbard-type multiband models for EtMe 3Sb[Pd(dmit) 2] 2 (where dmit is 1,3-dithiole-2-thione-4,5-dithiolate) and κ-(BEDT-TTF) 2Cu(NCS) 2 [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene] after a downfolding scheme based on the constrained random-phase approximation (cRPA) and maximally localized Wannier orbitals, together with the dimensional downfolding. In the Pd(dmit) 2 salt, the antibonding state of the highest occupied molecular orbital (HOMO) and the bonding/antibonding states of the lowest unoccupied molecular orbital (LUMO) are considered to be the orbital degrees of freedom, while, in the κ-BEDT-TTF salt, the HOMO-antibonding/bonding states are considered. Accordingly, a three-band model for the Pd(dmit) 2 salt and a two-band model for the κ-(BEDT-TTF) salt are derived. We derive single-band models for the HOMO-antibonding state for both of the compounds as well. The HOMO antibonding band of the Pd(dmit) 2 salt has a triangular structure of the transfers with a one-dimensional anisotropy, in contrast to the nearly equilateral triangular structure predicted in the extended Hückel results. The ratio of the larger interchain transfer t b to the intrachain transfer t a is around t b/t a∼0.82. Our calculated screened onsite interaction U and the largest offsite interaction V are ∼0.7 and ∼0.23 eV, respectively, for EtMe 3Sb[Pd(dmit) 2] 2 and ∼0.8 and ∼0.2 eV for κ-(BEDT-TTF) 2Cu(NCS) 2. These values are large enough compared to transfers t as ∼55 meV for the Pd(dmit) 2 salt and ∼65 meV for the κ-BEDT-TTF one, and the resulting large correlation strength (U-V)/t∼10 indicates that the present compounds are classified as the strongly correlated electron systems. In addition, the validity whether the present multiband model can be reduced to the single-band model for the HOMO-antibonding state, widely accepted in the literature, is discussed. For this purpose, we estimated the order of vertex corrections ignored in the cRPA downfolding to the single-band model, which is given by W′/D, where W′ is a full-screened-interaction matrix element between the HOMO-antibonding and other bands away from the Fermi level (namely, HOMO-bonding or LUMO-bonding/antibonding bands), whereas D is the energy distance between the Fermi level and the bands away from the Fermi level. In the present materials, W′/D estimated as 0.3-0.5 signals a substantial correction and thus the exchange process between the low-energy HOMO-antibonding and other bands away from the Fermi level may play a key role to the low-energy ground state. This supports that the minimal models to describe the low-energy phenomena of the organic compounds are the multiband models and may not be reduced to the single-band model.

Original languageEnglish
Article number205117
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume86
Issue number20
DOIs
Publication statusPublished - 2012 Nov 16
Externally publishedYes

Fingerprint

Molecular orbitals
molecular orbitals
Salts
Fermi level
salts
energy
BEDT-TTF
orbitals
interactions
Organic compounds
Ground state
approximation
organic compounds
Anisotropy
apexes
degrees of freedom
Electrons
anisotropy
ground state

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Cite this

@article{16d5555935684658aa9bc3448c0ebf43,
title = "Ab initio two-dimensional multiband low-energy models of EtMe 3Sb[Pd(dmit) 2] 2 and κ-(BEDT-TTF) 2Cu(NCS) 2 with comparisons to single-band models",
abstract = "We present ab initio two-dimensional extended Hubbard-type multiband models for EtMe 3Sb[Pd(dmit) 2] 2 (where dmit is 1,3-dithiole-2-thione-4,5-dithiolate) and κ-(BEDT-TTF) 2Cu(NCS) 2 [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene] after a downfolding scheme based on the constrained random-phase approximation (cRPA) and maximally localized Wannier orbitals, together with the dimensional downfolding. In the Pd(dmit) 2 salt, the antibonding state of the highest occupied molecular orbital (HOMO) and the bonding/antibonding states of the lowest unoccupied molecular orbital (LUMO) are considered to be the orbital degrees of freedom, while, in the κ-BEDT-TTF salt, the HOMO-antibonding/bonding states are considered. Accordingly, a three-band model for the Pd(dmit) 2 salt and a two-band model for the κ-(BEDT-TTF) salt are derived. We derive single-band models for the HOMO-antibonding state for both of the compounds as well. The HOMO antibonding band of the Pd(dmit) 2 salt has a triangular structure of the transfers with a one-dimensional anisotropy, in contrast to the nearly equilateral triangular structure predicted in the extended H{\"u}ckel results. The ratio of the larger interchain transfer t b to the intrachain transfer t a is around t b/t a∼0.82. Our calculated screened onsite interaction U and the largest offsite interaction V are ∼0.7 and ∼0.23 eV, respectively, for EtMe 3Sb[Pd(dmit) 2] 2 and ∼0.8 and ∼0.2 eV for κ-(BEDT-TTF) 2Cu(NCS) 2. These values are large enough compared to transfers t as ∼55 meV for the Pd(dmit) 2 salt and ∼65 meV for the κ-BEDT-TTF one, and the resulting large correlation strength (U-V)/t∼10 indicates that the present compounds are classified as the strongly correlated electron systems. In addition, the validity whether the present multiband model can be reduced to the single-band model for the HOMO-antibonding state, widely accepted in the literature, is discussed. For this purpose, we estimated the order of vertex corrections ignored in the cRPA downfolding to the single-band model, which is given by W′/D, where W′ is a full-screened-interaction matrix element between the HOMO-antibonding and other bands away from the Fermi level (namely, HOMO-bonding or LUMO-bonding/antibonding bands), whereas D is the energy distance between the Fermi level and the bands away from the Fermi level. In the present materials, W′/D estimated as 0.3-0.5 signals a substantial correction and thus the exchange process between the low-energy HOMO-antibonding and other bands away from the Fermi level may play a key role to the low-energy ground state. This supports that the minimal models to describe the low-energy phenomena of the organic compounds are the multiband models and may not be reduced to the single-band model.",
author = "Kazuma Nakamura and Yoshihide Yoshimoto and Masatoshi Imada",
year = "2012",
month = "11",
day = "16",
doi = "10.1103/PhysRevB.86.205117",
language = "English",
volume = "86",
journal = "Physical Review B-Condensed Matter",
issn = "0163-1829",
publisher = "American Institute of Physics Publising LLC",
number = "20",

}

TY - JOUR

T1 - Ab initio two-dimensional multiband low-energy models of EtMe 3Sb[Pd(dmit) 2] 2 and κ-(BEDT-TTF) 2Cu(NCS) 2 with comparisons to single-band models

AU - Nakamura, Kazuma

AU - Yoshimoto, Yoshihide

AU - Imada, Masatoshi

PY - 2012/11/16

Y1 - 2012/11/16

N2 - We present ab initio two-dimensional extended Hubbard-type multiband models for EtMe 3Sb[Pd(dmit) 2] 2 (where dmit is 1,3-dithiole-2-thione-4,5-dithiolate) and κ-(BEDT-TTF) 2Cu(NCS) 2 [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene] after a downfolding scheme based on the constrained random-phase approximation (cRPA) and maximally localized Wannier orbitals, together with the dimensional downfolding. In the Pd(dmit) 2 salt, the antibonding state of the highest occupied molecular orbital (HOMO) and the bonding/antibonding states of the lowest unoccupied molecular orbital (LUMO) are considered to be the orbital degrees of freedom, while, in the κ-BEDT-TTF salt, the HOMO-antibonding/bonding states are considered. Accordingly, a three-band model for the Pd(dmit) 2 salt and a two-band model for the κ-(BEDT-TTF) salt are derived. We derive single-band models for the HOMO-antibonding state for both of the compounds as well. The HOMO antibonding band of the Pd(dmit) 2 salt has a triangular structure of the transfers with a one-dimensional anisotropy, in contrast to the nearly equilateral triangular structure predicted in the extended Hückel results. The ratio of the larger interchain transfer t b to the intrachain transfer t a is around t b/t a∼0.82. Our calculated screened onsite interaction U and the largest offsite interaction V are ∼0.7 and ∼0.23 eV, respectively, for EtMe 3Sb[Pd(dmit) 2] 2 and ∼0.8 and ∼0.2 eV for κ-(BEDT-TTF) 2Cu(NCS) 2. These values are large enough compared to transfers t as ∼55 meV for the Pd(dmit) 2 salt and ∼65 meV for the κ-BEDT-TTF one, and the resulting large correlation strength (U-V)/t∼10 indicates that the present compounds are classified as the strongly correlated electron systems. In addition, the validity whether the present multiband model can be reduced to the single-band model for the HOMO-antibonding state, widely accepted in the literature, is discussed. For this purpose, we estimated the order of vertex corrections ignored in the cRPA downfolding to the single-band model, which is given by W′/D, where W′ is a full-screened-interaction matrix element between the HOMO-antibonding and other bands away from the Fermi level (namely, HOMO-bonding or LUMO-bonding/antibonding bands), whereas D is the energy distance between the Fermi level and the bands away from the Fermi level. In the present materials, W′/D estimated as 0.3-0.5 signals a substantial correction and thus the exchange process between the low-energy HOMO-antibonding and other bands away from the Fermi level may play a key role to the low-energy ground state. This supports that the minimal models to describe the low-energy phenomena of the organic compounds are the multiband models and may not be reduced to the single-band model.

AB - We present ab initio two-dimensional extended Hubbard-type multiband models for EtMe 3Sb[Pd(dmit) 2] 2 (where dmit is 1,3-dithiole-2-thione-4,5-dithiolate) and κ-(BEDT-TTF) 2Cu(NCS) 2 [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene] after a downfolding scheme based on the constrained random-phase approximation (cRPA) and maximally localized Wannier orbitals, together with the dimensional downfolding. In the Pd(dmit) 2 salt, the antibonding state of the highest occupied molecular orbital (HOMO) and the bonding/antibonding states of the lowest unoccupied molecular orbital (LUMO) are considered to be the orbital degrees of freedom, while, in the κ-BEDT-TTF salt, the HOMO-antibonding/bonding states are considered. Accordingly, a three-band model for the Pd(dmit) 2 salt and a two-band model for the κ-(BEDT-TTF) salt are derived. We derive single-band models for the HOMO-antibonding state for both of the compounds as well. The HOMO antibonding band of the Pd(dmit) 2 salt has a triangular structure of the transfers with a one-dimensional anisotropy, in contrast to the nearly equilateral triangular structure predicted in the extended Hückel results. The ratio of the larger interchain transfer t b to the intrachain transfer t a is around t b/t a∼0.82. Our calculated screened onsite interaction U and the largest offsite interaction V are ∼0.7 and ∼0.23 eV, respectively, for EtMe 3Sb[Pd(dmit) 2] 2 and ∼0.8 and ∼0.2 eV for κ-(BEDT-TTF) 2Cu(NCS) 2. These values are large enough compared to transfers t as ∼55 meV for the Pd(dmit) 2 salt and ∼65 meV for the κ-BEDT-TTF one, and the resulting large correlation strength (U-V)/t∼10 indicates that the present compounds are classified as the strongly correlated electron systems. In addition, the validity whether the present multiband model can be reduced to the single-band model for the HOMO-antibonding state, widely accepted in the literature, is discussed. For this purpose, we estimated the order of vertex corrections ignored in the cRPA downfolding to the single-band model, which is given by W′/D, where W′ is a full-screened-interaction matrix element between the HOMO-antibonding and other bands away from the Fermi level (namely, HOMO-bonding or LUMO-bonding/antibonding bands), whereas D is the energy distance between the Fermi level and the bands away from the Fermi level. In the present materials, W′/D estimated as 0.3-0.5 signals a substantial correction and thus the exchange process between the low-energy HOMO-antibonding and other bands away from the Fermi level may play a key role to the low-energy ground state. This supports that the minimal models to describe the low-energy phenomena of the organic compounds are the multiband models and may not be reduced to the single-band model.

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