An optimally tuned range-separated hybrid starting point for ab initio GW plus Bethe–Salpeter equation calculations of molecules
Abstract
The ab initio GW plus Bethe–Salpeter equation (GW-BSE, where G is the one particle Green's function and W is the screened Coulomb interaction) approach has emerged as a leading method for predicting excitations in both solids and molecules with a predictive power contingent upon several factors. Among these factors are the (1) generalized Kohn–Sham eigensystem used to construct the GW self-energy and to solve the BSE and (2) the efficacy and suitability of the Tamm–Dancoff approximation. Here, we present a detailed benchmark study of low-lying singlet excitations from a generalized Kohn–Sham (gKS) starting point based on an optimally tuned range-separated hybrid (OTRSH) functional. We show that the use of this gKS starting point with one-shot G0W0 and G0W0-BSE leads to the lowest mean absolute errors (MAEs) and mean signed errors (MSEs), with respect to high-accuracy reference values, demonstrated in the literature thus far for the ionization potentials of the GW100 benchmark set and for low-lying neutral excitations of Thiel’s set molecules in the gas phase, without the need for self-consistency. The MSEs and MAEs of one-shot G0W0-BSE@OTRSH excitation energies are comparable to or lower than those obtained with other functional starting points after self-consistency. Additionally, we compare these results withmore »
- Authors:
- Publication Date:
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 1882232
- Grant/Contract Number:
- AC02-05CH11231; 2022-096018
- Resource Type:
- Publisher's Accepted Manuscript
- Journal Name:
- Journal of Chemical Physics
- Additional Journal Information:
- Journal Name: Journal of Chemical Physics Journal Volume: 157 Journal Issue: 7; Journal ID: ISSN 0021-9606
- Publisher:
- American Institute of Physics
- Country of Publication:
- United States
- Language:
- English
Citation Formats
McKeon, Caroline A., Hamed, Samia M., Bruneval, Fabien, and Neaton, Jeffrey B. An optimally tuned range-separated hybrid starting point for ab initio GW plus Bethe–Salpeter equation calculations of molecules. United States: N. p., 2022.
Web. doi:10.1063/5.0097582.
McKeon, Caroline A., Hamed, Samia M., Bruneval, Fabien, & Neaton, Jeffrey B. An optimally tuned range-separated hybrid starting point for ab initio GW plus Bethe–Salpeter equation calculations of molecules. United States. https://doi.org/10.1063/5.0097582
McKeon, Caroline A., Hamed, Samia M., Bruneval, Fabien, and Neaton, Jeffrey B. Wed .
"An optimally tuned range-separated hybrid starting point for ab initio GW plus Bethe–Salpeter equation calculations of molecules". United States. https://doi.org/10.1063/5.0097582.
@article{osti_1882232,
title = {An optimally tuned range-separated hybrid starting point for ab initio GW plus Bethe–Salpeter equation calculations of molecules},
author = {McKeon, Caroline A. and Hamed, Samia M. and Bruneval, Fabien and Neaton, Jeffrey B.},
abstractNote = {The ab initio GW plus Bethe–Salpeter equation (GW-BSE, where G is the one particle Green's function and W is the screened Coulomb interaction) approach has emerged as a leading method for predicting excitations in both solids and molecules with a predictive power contingent upon several factors. Among these factors are the (1) generalized Kohn–Sham eigensystem used to construct the GW self-energy and to solve the BSE and (2) the efficacy and suitability of the Tamm–Dancoff approximation. Here, we present a detailed benchmark study of low-lying singlet excitations from a generalized Kohn–Sham (gKS) starting point based on an optimally tuned range-separated hybrid (OTRSH) functional. We show that the use of this gKS starting point with one-shot G0W0 and G0W0-BSE leads to the lowest mean absolute errors (MAEs) and mean signed errors (MSEs), with respect to high-accuracy reference values, demonstrated in the literature thus far for the ionization potentials of the GW100 benchmark set and for low-lying neutral excitations of Thiel’s set molecules in the gas phase, without the need for self-consistency. The MSEs and MAEs of one-shot G0W0-BSE@OTRSH excitation energies are comparable to or lower than those obtained with other functional starting points after self-consistency. Additionally, we compare these results with linear-response time-dependent density functional theory (TDDFT) calculations and find GW-BSE to be superior to TDDFT when calculations are based on the same exchange-correlation functional. This work demonstrates tuned range-separated hybrids used in combination with GW and GW-BSE can greatly suppress starting point dependence for molecules, leading to accuracy similar to that for higher-order wavefunction-based theories for molecules without the need for costlier iterations to self-consistency.},
doi = {10.1063/5.0097582},
journal = {Journal of Chemical Physics},
number = 7,
volume = 157,
place = {United States},
year = {Wed Aug 17 00:00:00 EDT 2022},
month = {Wed Aug 17 00:00:00 EDT 2022}
}
https://doi.org/10.1063/5.0097582
Works referenced in this record:
Ionized, electron-attached, and excited states of molecular systems with spin–orbit coupling: Two-component GW and Bethe–Salpeter implementations
journal, May 2019
- Holzer, Christof; Klopper, Wim
- The Journal of Chemical Physics, Vol. 150, Issue 20
Screening mixing GW/Bethe–Salpeter approach for triplet states of organic molecules
journal, September 2018
- Ziaei, Vafa; Bredow, Thomas
- Journal of Physics: Condensed Matter, Vol. 30, Issue 39
A systematic benchmark of the ab initio Bethe-Salpeter equation approach for low-lying optical excitations of small organic molecules
journal, June 2015
- Bruneval, Fabien; Hamed, Samia M.; Neaton, Jeffrey B.
- The Journal of Chemical Physics, Vol. 142, Issue 24
Influence of solution phase environmental heterogeneity and fluctuations on vibronic spectra: Perylene diimide molecular chromophore complexes in solution
journal, June 2021
- Kumar, Manav; Provazza, Justin; Coker, David F.
- The Journal of Chemical Physics, Vol. 154, Issue 22
Qualitatively Incorrect Features in the TDDFT Spectrum of Thiophene-Based Compounds
journal, December 2014
- Prlj, Antonio; Curchod, Basile F. E.; Fabrizio, Alberto
- The Journal of Physical Chemistry Letters, Vol. 6, Issue 1
Benchmarking TD-DFT and Wave Function Methods for Oscillator Strengths and Excited-State Dipole Moments
journal, January 2021
- Sarkar, Rudraditya; Boggio-Pasqua, Martial; Loos, Pierre-François
- Journal of Chemical Theory and Computation, Vol. 17, Issue 2
Evaluating the GW Approximation with CCSD(T) for Charged Excitations Across the Oligoacenes
journal, May 2016
- Rangel, Tonatiuh; Hamed, Samia M.; Bruneval, Fabien
- Journal of Chemical Theory and Computation, Vol. 12, Issue 6
Exact results for the charge and spin densities, exchange-correlation potentials, and density-functional eigenvalues
journal, March 1985
- Almbladh, C. -O.; von Barth, U.
- Physical Review B, Vol. 31, Issue 6
Outer-valence Electron Spectra of Prototypical Aromatic Heterocycles from an Optimally Tuned Range-Separated Hybrid Functional
journal, April 2014
- Egger, David A.; Weissman, Shira; Refaely-Abramson, Sivan
- Journal of Chemical Theory and Computation, Vol. 10, Issue 5
Accurate Ionization Potentials and Electron Affinities of Acceptor Molecules III: A Benchmark of GW Methods
journal, January 2016
- Knight, Joseph W.; Wang, Xiaopeng; Gallandi, Lukas
- Journal of Chemical Theory and Computation, Vol. 12, Issue 2
The GW Miracle in Many-Body Perturbation Theory for the Ionization Potential of Molecules
journal, December 2021
- Bruneval, Fabien; Dattani, Nike; van Setten, Michiel J.
- Frontiers in Chemistry, Vol. 9
Accurate Ionization Potentials and Electron Affinities of Acceptor Molecules II: Non-Empirically Tuned Long-Range Corrected Hybrid Functionals
journal, January 2016
- Gallandi, Lukas; Marom, Noa; Rinke, Patrick
- Journal of Chemical Theory and Computation, Vol. 12, Issue 2
molgw 1: Many-body perturbation theory software for atoms, molecules, and clusters
journal, November 2016
- Bruneval, Fabien; Rangel, Tonatiuh; Hamed, Samia M.
- Computer Physics Communications, Vol. 208
Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen
journal, January 1989
- Dunning, Thom H.
- The Journal of Chemical Physics, Vol. 90, Issue 2
Combining localized orbital scaling correction and Bethe–Salpeter equation for accurate excitation energies
journal, April 2022
- Li, Jiachen; Jin, Ye; Su, Neil Qiang
- The Journal of Chemical Physics, Vol. 156, Issue 15
Does a Molecule-Specific Density Functional Give an Accurate Electron Density? The Challenging Case of the CuCl Electric Field Gradient
journal, February 2012
- Srebro, Monika; Autschbach, Jochen
- The Journal of Physical Chemistry Letters, Vol. 3, Issue 5
Excited-State Properties of Molecular Solids from First Principles
journal, May 2016
- Kronik, Leeor; Neaton, Jeffrey B.
- Annual Review of Physical Chemistry, Vol. 67, Issue 1
Optimum Exchange for Calculation of Excitation Energies and Hyperpolarizabilities of Organic Electro-optic Chromophores
journal, August 2014
- Garrett, Kerry; Sosa Vazquez, XochitlA; Egri, Shawn B.
- Journal of Chemical Theory and Computation, Vol. 10, Issue 9
Dye-Sensitized Solar Cells: Fundamentals and Current Status
journal, November 2018
- Sharma, Khushboo; Sharma, Vinay; Sharma, S. S.
- Nanoscale Research Letters, Vol. 13, Issue 1
Accurate description of the electronic structure of organic semiconductors by GW methods
journal, February 2017
- Marom, Noa
- Journal of Physics: Condensed Matter, Vol. 29, Issue 10
Taking Up the Cyanine Challenge with Quantum Tools
journal, February 2015
- Le Guennic, Boris; Jacquemin, Denis
- Accounts of Chemical Research, Vol. 48, Issue 3
Too big, too small, or just right? A benchmark assessment of density functional theory for predicting the spatial extent of the electron density of small chemical systems
journal, February 2021
- Hait, Diptarka; Liang, Yu Hsuan; Head-Gordon, Martin
- The Journal of Chemical Physics, Vol. 154, Issue 7
Reliable Prediction of Charge Transfer Excitations in Molecular Complexes Using Time-Dependent Density Functional Theory
journal, March 2009
- Stein, Tamar; Kronik, Leeor; Baer, Roi
- Journal of the American Chemical Society, Vol. 131, Issue 8
Benchmarks for electronically excited states: CASPT2, CC2, CCSD, and CC3
journal, April 2008
- Schreiber, Marko; Silva-Junior, Mario R.; Sauer, Stephan P. A.
- The Journal of Chemical Physics, Vol. 128, Issue 13
TD-DFT benchmarks: A review
journal, April 2013
- Laurent, Adèle D.; Jacquemin, Denis
- International Journal of Quantum Chemistry, Vol. 113, Issue 17
Time-Dependent Density Functional Response Theory for Molecules
book, November 1995
- Casida, Mark E.
- Recent Advances in Density Functional Methods
A new hybrid exchange–correlation functional using the Coulomb-attenuating method (CAM-B3LYP)
journal, July 2004
- Yanai, Takeshi; Tew, David P.; Handy, Nicholas C.
- Chemical Physics Letters, Vol. 393, Issue 1-3, p. 51-57
Long-Range Corrected DFT Meets GW : Vibrationally Resolved Photoelectron Spectra from First Principles
journal, October 2015
- Gallandi, Lukas; Körzdörfer, Thomas
- Journal of Chemical Theory and Computation, Vol. 11, Issue 11
Benchmarking the Bethe–Salpeter Formalism on a Standard Organic Molecular Set
journal, June 2015
- Jacquemin, Denis; Duchemin, Ivan; Blase, Xavier
- Journal of Chemical Theory and Computation, Vol. 11, Issue 7
Assessment of the Accuracy of the Bethe–Salpeter (BSE/ GW ) Oscillator Strengths
journal, July 2016
- Jacquemin, Denis; Duchemin, Ivan; Blondel, Aymeric
- Journal of Chemical Theory and Computation, Vol. 12, Issue 8
Fundamentals of Time-Dependent Density Functional Theory
book, January 2012
- Marques, Miguel A. L.; Maitra, Neepa T.; Nogueira, Fernando M. S.
- Lecture Notes in Physics
All-electron ab initio Bethe-Salpeter equation approach to neutral excitations in molecules with numeric atom-centered orbitals
journal, January 2020
- Liu, Chi; Kloppenburg, Jan; Yao, Yi
- The Journal of Chemical Physics, Vol. 152, Issue 4
Coupled-cluster reference values for the GW27 and GW100 test sets for the assessment of GW methods
journal, March 2015
- Krause, Katharina; Harding, Michael E.; Klopper, Wim
- Molecular Physics, Vol. 113, Issue 13-14
Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy
journal, January 2005
- Weigend, Florian; Ahlrichs, Reinhart
- Physical Chemistry Chemical Physics, Vol. 7, Issue 18, p. 3297-3305
Quasiparticle Spectra from a Nonempirical Optimally Tuned Range-Separated Hybrid Density Functional
journal, November 2012
- Refaely-Abramson, Sivan; Sharifzadeh, Sahar; Govind, Niranjan
- Physical Review Letters, Vol. 109, Issue 22
Nanoscale Strategies for Light Harvesting
journal, March 2016
- Kundu, Simanta; Patra, Amitava
- Chemical Reviews, Vol. 117, Issue 2
Excitation energies in density functional theory: An evaluation and a diagnostic test
journal, January 2008
- Peach, Michael J. G.; Benfield, Peter; Helgaker, Trygve
- The Journal of Chemical Physics, Vol. 128, Issue 4
A long-range-corrected density functional that performs well for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states
journal, February 2009
- Rohrdanz, Mary A.; Martins, Katie M.; Herbert, John M.
- The Journal of Chemical Physics, Vol. 130, Issue 5
The Quest for Highly Accurate Excitation Energies: A Computational Perspective
journal, March 2020
- Loos, Pierre-François; Scemama, Anthony; Jacquemin, Denis
- The Journal of Physical Chemistry Letters, Vol. 11, Issue 6
A well-tempered density functional theory of electrons in molecules
journal, January 2007
- Livshits, Ester; Baer, Roi
- Physical Chemistry Chemical Physics, Vol. 9, Issue 23
Exciton-Plasmon States in Nanoscale Materials: Breakdown of the Tamm−Dancoff Approximation
journal, August 2009
- Grüning, Myrta; Marini, Andrea; Gonze, Xavier
- Nano Letters, Vol. 9, Issue 8
GW 100: Benchmarking G 0 W 0 for Molecular Systems
journal, November 2015
- van Setten, Michiel J.; Caruso, Fabio; Sharifzadeh, Sahar
- Journal of Chemical Theory and Computation, Vol. 11, Issue 12
Size-Dependence of Nonempirically Tuned DFT Starting Points for G 0 W 0 Applied to π-Conjugated Molecular Chains
journal, September 2017
- Bois, Juliana; Körzdörfer, Thomas
- Journal of Chemical Theory and Computation, Vol. 13, Issue 10
Random-Phase Approximation Methods
journal, May 2017
- Chen, Guo P.; Voora, Vamsee K.; Agee, Matthew M.
- Annual Review of Physical Chemistry, Vol. 68, Issue 1
Localization and Delocalization Errors in Density Functional Theory and Implications for Band-Gap Prediction
journal, April 2008
- Mori-Sánchez, Paula; Cohen, Aron J.; Yang, Weitao
- Physical Review Letters, Vol. 100, Issue 14
Improving virtual Kohn–Sham orbitals and eigenvalues: Application to excitation energies and static polarizabilities
journal, December 1998
- Tozer, David J.; Handy, Nicholas C.
- The Journal of Chemical Physics, Vol. 109, Issue 23
The GW method
journal, March 1998
- Aryasetiawan, F.; Gunnarsson, O.
- Reports on Progress in Physics, Vol. 61, Issue 3
Charge-Transfer Excitations: A Challenge for Time-Dependent Density Functional Theory That Has Been Met
journal, May 2017
- Kümmel, Stephan
- Advanced Energy Materials, Vol. 7, Issue 16
Benchmarks of electronically excited states: Basis set effects on CASPT2 results
journal, November 2010
- Silva-Junior, Mario R.; Schreiber, Marko; Sauer, Stephan P. A.
- The Journal of Chemical Physics, Vol. 133, Issue 17
Density Functional Theory with Correct Long-Range Asymptotic Behavior
journal, February 2005
- Baer, Roi; Neuhauser, Daniel
- Physical Review Letters, Vol. 94, Issue 4
Failure of Time-Dependent Density Functional Theory for Long-Range Charge-Transfer Excited States: The Zincbacteriochlorin−Bacteriochlorin and Bacteriochlorophyll−Spheroidene Complexes
journal, March 2004
- Dreuw, Andreas; Head-Gordon, Martin
- Journal of the American Chemical Society, Vol. 126, Issue 12
Fractional charge perspective on the band gap in density-functional theory
journal, March 2008
- Cohen, Aron J.; Mori-Sánchez, Paula; Yang, Weitao
- Physical Review B, Vol. 77, Issue 11
Cross-Comparisons between Experiment, TD-DFT, CC, and ADC for Transition Energies
journal, June 2019
- Suellen, Cinthia; Freitas, Renato Garcia; Loos, Pierre-François
- Journal of Chemical Theory and Computation, Vol. 15, Issue 8
A Mountaineering Strategy to Excited States: Highly Accurate Energies and Benchmarks for Medium Sized Molecules
journal, January 2020
- Loos, Pierre-François; Lipparini, Filippo; Boggio-Pasqua, Martial
- Journal of Chemical Theory and Computation, Vol. 16, Issue 3
Overcoming Low Orbital Overlap and Triplet Instability Problems in TDDFT
journal, September 2012
- Peach, Michael J. G.; Tozer, David J.
- The Journal of Physical Chemistry A, Vol. 116, Issue 39
Benchmarking the Starting Points of the GW Approximation for Molecules
journal, December 2012
- Bruneval, Fabien; Marques, Miguel A. L.
- Journal of Chemical Theory and Computation, Vol. 9, Issue 1
Extensive TD-DFT Benchmark: Singlet-Excited States of Organic Molecules
journal, August 2009
- Jacquemin, Denis; Wathelet, Valérie; Perpète, Eric A.
- Journal of Chemical Theory and Computation, Vol. 5, Issue 9
Accuracy Assessment of GW Starting Points for Calculating Molecular Excitation Energies Using the Bethe–Salpeter Formalism
journal, March 2018
- Gui, Xin; Holzer, Christof; Klopper, Wim
- Journal of Chemical Theory and Computation, Vol. 14, Issue 4
Equation of Motion for the Solvent Polarization Apparent Charges in the Polarizable Continuum Model: Application to Real-Time TDDFT
journal, December 2014
- Corni, Stefano; Pipolo, Silvio; Cammi, Roberto
- The Journal of Physical Chemistry A, Vol. 119, Issue 21
Koopmans-Compliant Functionals and Potentials and Their Application to the GW100 Test Set
journal, January 2019
- Colonna, Nicola; Nguyen, Ngoc Linh; Ferretti, Andrea
- Journal of Chemical Theory and Computation, Vol. 15, Issue 3
Spin-orbit relativistic long-range corrected time-dependent density functional theory for investigating spin-forbidden transitions in photochemical reactions
journal, December 2011
- Nakata, Ayako; Tsuneda, Takao; Hirao, Kimihiko
- The Journal of Chemical Physics, Vol. 135, Issue 22
Strategy for finding a reliable starting point for demonstrated for molecules
journal, July 2012
- Körzdörfer, Thomas; Marom, Noa
- Physical Review B, Vol. 86, Issue 4
First principles theoretical spectroscopy of methylene blue: Between limitations of time-dependent density functional theory approximations and its realistic description in the solvent
journal, January 2021
- de Queiroz, Thiago B.; de Figueroa, Erick R.; Coutinho-Neto, Maurício D.
- The Journal of Chemical Physics, Vol. 154, Issue 4
The Bethe–Salpeter Equation Formalism: From Physics to Chemistry
journal, August 2020
- Blase, Xavier; Duchemin, Ivan; Jacquemin, Denis
- The Journal of Physical Chemistry Letters, Vol. 11, Issue 17
Analytical energy gradients of Coulomb-attenuated time-dependent density functional methods for excited states
journal, May 2010
- Nguyen, Kiet A.; Day, Paul N.; Pachter, Ruth
- International Journal of Quantum Chemistry, Vol. 110, Issue 12
Evaluation of Single-Reference DFT-Based Approaches for the Calculation of Spectroscopic Signatures of Excited States Involved in Singlet Fission
journal, September 2020
- Han, Jie; Rehn, Dirk Robert; Buckup, Tiago
- The Journal of Physical Chemistry A, Vol. 124, Issue 41
An assessment of low-lying excitation energies and triplet instabilities of organic molecules with an ab initio Bethe-Salpeter equation approach and the Tamm-Dancoff approximation
journal, May 2017
- Rangel, Tonatiuh; Hamed, Samia M.; Bruneval, Fabien
- The Journal of Chemical Physics, Vol. 146, Issue 19
Assessment of the Ab Initio Bethe–Salpeter Equation Approach for the Low-Lying Excitation Energies of Bacteriochlorophylls and Chlorophylls
journal, March 2021
- Hashemi, Zohreh; Leppert, Linn
- The Journal of Physical Chemistry A, Vol. 125, Issue 10
Excited-state electronic structure of molecules using many-body Green’s functions: Quasiparticles and electron–hole excitations with VOTCA-XTP
journal, March 2020
- Tirimbò, G.; Sundaram, V.; Çaylak, O.
- The Journal of Chemical Physics, Vol. 152, Issue 11
Density-Functional Theory for Time-Dependent Systems
journal, March 1984
- Runge, Erich; Gross, E. K. U.
- Physical Review Letters, Vol. 52, Issue 12
Excitation Gaps of Finite-Sized Systems from Optimally Tuned Range-Separated Hybrid Functionals
journal, April 2012
- Kronik, Leeor; Stein, Tamar; Refaely-Abramson, Sivan
- Journal of Chemical Theory and Computation, Vol. 8, Issue 5
Quantitative Accuracy in Calculating Charge Transfer State Energies in Solvated Molecular Complexes Using a Screened Range Separated Hybrid Functional within a Polarized Continuum Model
journal, June 2019
- Bhandari, Srijana; Dunietz, Barry D.
- Journal of Chemical Theory and Computation, Vol. 15, Issue 8
Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields
journal, November 1994
- Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.
- The Journal of Physical Chemistry, Vol. 98, Issue 45, p. 11623-11627
TD-DFT Performance for the Visible Absorption Spectra of Organic Dyes: Conventional versus Long-Range Hybrids
journal, November 2007
- Jacquemin, Denis; Perpète, Eric A.; Scuseria, Gustavo E.
- Journal of Chemical Theory and Computation, Vol. 4, Issue 1
From Biomass to a Renewable LiXC6O6 Organic Electrode for Sustainable Li-Ion Batteries
journal, April 2008
- Chen, Haiyan; Armand, Michel; Demailly, Gilles
- ChemSusChem, Vol. 1, Issue 4
Integral approximations for LCAO-SCF calculations
journal, October 1993
- Vahtras, O.; Almlöf, J.; Feyereisen, M. W.
- Chemical Physics Letters, Vol. 213, Issue 5-6
Excited-State Geometry Optimization of Small Molecules with Many-Body Green’s Functions Theory
journal, January 2021
- Çaylak, Onur; Baumeier, Björn
- Journal of Chemical Theory and Computation, Vol. 17, Issue 2
Time-Dependent Density Functional Theory
journal, June 2004
- Marques, M. A. L.; Gross, E. K. U.
- Annual Review of Physical Chemistry, Vol. 55, Issue 1
Koopmans’ springs to life
journal, December 2009
- Salzner, Ulrike; Baer, Roi
- The Journal of Chemical Physics, Vol. 131, Issue 23
Fundamental and excitation gaps in molecules of relevance for organic photovoltaics from an optimally tuned range-separated hybrid functional
journal, August 2011
- Refaely-Abramson, Sivan; Baer, Roi; Kronik, Leeor
- Physical Review B, Vol. 84, Issue 7