MATERIALS FOR ENERGYCMAST (Computational MAterials Science & Technology) Virtual Lab

www.afs.enea.it/project/cmast

Computational Materials Science

Hydrogen storage Projects:• AMPEA, Joint Programme on Advanced Materials and Processes for

Energy Application (EERA, European Energy Research Alliance)• COST Action MP1103: Nanostructured materials for solid-state

hydrogen storage (FP7 European cooperation in science and technology )• HYDROSTORE, Industria 2015 “Efficienza energetica”

Problem: MgH2 is a very promising material for hydrogen storage but hydrogen desorption has low kinetic and no efficient cycling. Metallic catalysts are used to speed up the desorption process.

Open questions:1) Which are the chemical and physical processes that drive, at the atomic scale,

the H desorption?2) Which is the most efficient catalyst to speed-up the desorption ?

Method:Quantum molecular dynamics simulations are used to model an Mg-MgH2 interface to accurately reproduce the hydrogen desorption. The interface is simulated imposing several external temperatures. The model is reliable because the desorption temperature is found in agreement with experiments. Moreover one Mg atom has been substitued by a catalyst (Fe, Pd, Ni, …) and the new desorption temperature is computed.

Catalytic effect of intermetallics in the Hydrogen desorption mechanism at the MgH2-Mg interface

S. Giusepponi (ENEA), M. Celino (ENEA)

Mg

MgH2

Mg-MgH2 interface

The model interface

The model interface with catalystT= 700 K

T= 800 K

T= 900 K

Blu are Mg atoms. Hydrogen atoms have different colours depending on the distance from the interface.

Photovoltaic applications:an European multiscale modeling infrastructure

Liquid

Projects:• SOPHIA - Research Infrastructures for Solar Energy Photovoltaic

Power, WP12 (FP7 INFRA-2010-1.1.22)

M. Celino (ENEA)

4-fold coordination

5 -fold coordination

6-7-fold coordination

A crystalline amorphous silicon has been heated up from the crystalline phase at low temperature till the melting and above. Rapid quench of the melt produces an amorphous atomic configuration.

AmorphousCrystalline

Results:1) Molecular dynamics code and computational

platform are available to partners2) Model of Hydrogenated a-Si has been

generated and characterized3) Electronic DOS, Optical Absorbance and

structural information are generated as input for the higher modeling scales.

Problem: In Europe it s lacking a common computational platform devoted to modeling in the field of photovoltaic applications. Moreover there is the need to gather in the same infrastructure all the numerical codes and organize them in such a way to simulate real PV systems with the accuratness of atomic scale approaches.

Open questions:1) How to gather all the numerical code in a multiscale fashion to simulate a PV

system starting form the atomic scale information ?2) Which are the software to be developed to exchange informations between two

diffent modeling scales ?

Method:ENEA is sharing its computational facilities, mainly the CRESCO platform, via Trans National Access mechanism to foreing parteners interested in developing PV studies by using high performance computing platforms. Moreover, quantum molecular dynamics code are available to interested partners. The consortium has chosen Hydrogenated a-Si as test case to the develop the multiscale modeling infrastructure.

QuenchingMelting

Electronic DOS Optical absorbance Structural information

Results:1) Hydrogen diffusion has been

computed2) The role of catalysts has been

understood3) The most efficient catalyst has

been selected.

Photovoltaic applications:optical properties of Si(111)2x1 surface isomers

C. Violante (Tor Vergata), A. Mosca Conte (Tor Vergata), O. Pulci (Tor Vergata), F. Bechstedt (IFTO, Jena, Germany)

Problem: The Si(111)2x1 is one of the most studied surfaces. Its reconstruction is describedby the Pandey model with a buckling of the topmost atoms. With relation to the sign of the buckling, there are two slightly different geometric structures (isomers), conventionally named positive buckling and negative buckling. STM measurements suggest that the positive buckling isomer is the stable configuration at room temperature, but a recent work, involving STS measurements, has shown the coexistence of both the isomers, at very low temperature,for highly n-doped Si(111)2x1 specimens.

Open questions:1) Which the stable configuration of the silicon (111) surface ?2) How the surface configuration affects the optical properties of the material ?

Method:Quantum calculation (DFT-LDA) to model the structure. GW to accurately compute the electronic structure and GW to determine the optimal properties with excitonic effects

Projects:• CLERMONT4 project : “Exciton-polaritons: Physics and

Applications “ (EU FP7, Marie Curie program PEOPLE).

Positive bucklingNegative buckling

Results:1) The two isomers are both energetic stable

local minima, almost degenerate in energy and separated by an energetic barrier

2) Differences in electronic structure and optical properties are evidenced: the RAS (reverse anisotropy spectroscopy) peak of the negatvie buckling isomer is more intense and redshifted by 0.2-0.3 eV with respect to positive buckling.

EXP 0.47eV EXP 0.83eV

Band structuresoptical properties

The surface can be further functionalized.