Publications by Paolo Umari | EPFL Graph Search

Koopmans Meets Bethe-Salpeter: Excitonic Optical Spectra without GW

Paolo Umari, Nicola Marzari, Nicola Colonna

The Bethe Salpeter equation (BSE) can be applied to compute from first-principles optical spectra that include the effects of screened electron hole interactions. As input, BSE calculations require single-particle states, quasiparticle energy levels, and t ...

AMER CHEMICAL SOC2019

SIMPLE code: Optical properties with optimal basis functions

Paolo Umari, Nicola Marzari, Gianluca Prandini

We present SIMPLE, a code developed to calculate optical properties of metallic and insulating extended systems using the optimal basis method originally proposed by E.L. Shirley in 1996. Two different approaches for the evaluation of the complex dielectri ...

ELSEVIER SCIENCE BV2019

Gauge Invariance of Thermal Transport Coefficients

Paolo Umari, Aris Marcolongo, Loris Ercole

Thermal transport coefficients are independent of the specific microscopic expression for the energy density and current from which they can be derived through the Green-Kubo formula. We discuss this independence in terms of a kind of gauge invariance resu ...

Springer/Plenum Publishers2016

First-principles investigation of organic photovoltaic materials C-60, C-70, [C-60]PCBM, and bis-[C-60]PCBM using a many-body G(0)W(0)-Lanczos approach

Paolo Umari, Nicola Marzari

We present a first-principles investigation of the excited-state properties of electron acceptors in organic photovoltaics including C-60, C-70, [6,6]-phenyl-C-61-butyric-acid-methyl-ester ([C-60] PCBM), and bis-[C-60] PCBM usingmany-body perturbation theo ...

Amer Physical Soc2015

Cation-Induced Band-Gap Tuning in Organohalide Perovskites: Interplay of Spin-Orbit Coupling and Octahedra Tilting

Michael Graetzel, Mohammad Khaja Nazeeruddin, Paolo Umari, Filippo de Angelis

Organohalide lead perovskites have revolutionized the scenario of emerging photovoltaic technologies. The prototype MAPbI(3) perovskite (MA = CH3NH3+) has dominated the field, despite only harvesting photons above 750 nm (similar to 1.6 eV). Intensive rese ...

American Chemical Society2014

Medium-range structure of vitreous SiO2 obtained through first-principles investigation of vibrational spectra

Alfredo Pasquarello, Paolo Umari, Luigi Giacomazzi

Using a density-functional framework, we investigate the vibrational spectra of vitreous SiO2 to determine to what extent these spectra provide information about the medium-range structure of the oxide network. We carry out a comparative study involving th ...

2009