Density Functional Tight-Binding Model for Lithium-Silicon Alloys

MARÍA BELÉN OVIEDO; FRANCISCO FERNÁNDEZ; MANUEL OTERO; EZEQUIEL PEDRO MARCO LEIVA; SERGIO ALEXIS PAZ

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 2023 vol. 127 p. 2637 - 2645

1089-5639

The predictive power of molecular dynamic simulations is mainly restricted bythe time scale and model accuracy. Many systems of current relevance are of suchcomplexity that requires addressing both issues simultaneously. This is the case ofsilicon electrodes in Li-ion batteries, where different LixSi alloys are formed duringcharge/discharge cycles. While first-principles treatments for this system are seriouslylimited by the computational cost of exploring its large conformational space, classicalforce-fields are not transferable enough to represent it accurately. Density FunctionalTight-Binding (DFTB) is an intermediate complexity approach capable of capturingthe electronic nature of different environments with a relatively low computationalcost. In this work, we present a new set of DFTB parameters suited to model amorphous LixSi alloys. The latter is the usual finding upon cycling the Si electrodes in thepresence of Li-ions. The model parameters are constructed with a particular emphasis on their transferability for the entire LixSi composition range. This is achieved by introducing a new optimization procedure that weights stoichiometries differently toimprove the prediction of their formation energies. The resulting model is shown to berobust for predicting crystal and amorphous structures for the different compositions,giving excellent agreement with DFT calculations and outperforming state-of-the-artReaxFF potentials.