Presentation on theme: "Daniel Sánchez-Portal"— Presentation transcript:
1 Daniel Sánchez-Portal Calculation of optical properties and macroscopic polarization with SIESTADaniel Sánchez-PortalCentro de Física de Materiales, Centro Mixto CSIC-UPV/EHU,San Sebastián, SpainEfficient density-functional calculations with atomic orbtitals: a hands-on tutorial on the SIESTA codeCECAM TutorialLyon, June 18-22
2 Polarizability Molecule Exact many body wavefunctions and eigenvalues Approximation with Kohn-Sham orbitals and eigenvalues
3 Dielectric function in solids Without local field correctionsUnfortunately there is no way to apply this formula to a solidPosition operator is ill-definedfor extended wavefunctions
5 A word of caution for non-local potentials No problem: localized objects
6 Thomas-Reiche-Kuhn or f-sum rule Drude term for metals (ω0)
7 Parameters and inputOpticalCalculation : default .false., set to .true.Optical.NumberOfBands : all of them used if not specified%block Optical.Meshn n n3%endblock Optical.MeshOptical.Broaden: small “artificial” broadening, 0.X eVOptical.PolarizationType: polarized, unpolarized, polycrystal%block Optical.VectorEx Ey Ez%endblock Optical.VectorEither E, electric fieldor k, propagation vector
8 Optical.Vector Polarized: Unpolarized: Polycrystal: Average over three spatial directions
9 What is left out in this approach *Classical collective modes (plasmons). They can beincluded at the RPA level. Important at low energiesfor small systems, not that much for bulk.*Excitonic effects (electron-hole interaccion). Quite hardto include*Spectrum beyon Kohn-Sham approx.At the moment just the “scissor operator” to correct excitationenergies.
10 SIESTA Diamond and Silicon Silicon Diamond PW, CASTEP G.F. Bertsch et al.Phys.Rev. B 62, 7998 (2000).SIESTASiliconDiamondPW, CASTEPDZP basis set (26 bands)
12 Optical response of 4-Å diameter SWCNT with SIESTA Testing the accuaracy of SIESTA band structures on graphene:Including a diffuse 3s orbital we have perfect with PW up to 6 eVAdding an additional 3p shell the agreement is extended to eVIn fact, ...Our band structures for the 4-Å are in very niceagreement with the PW calculations of Li et al.
13 Optical response of 4-Å diameter SWCNT with SIESTA (cont.) (5,0)(4,2)(3,3)(3,3)(4,2)(5,0)All channels occupied1:0.7:0.2(5,0):(3,3):(4,2)f=2x10-4