Self-Learning Method for Construction of Analytical Interatomic Potentials to Describe Laser-Excited Materials

Abstract

We develop an electronic-temperature dependent interatomic potential Φ(T e ) for unexcited and laser-excited silicon. The potential is designed to reproduce ab initio molecular dynamics simulations by requiring force-and energy matching for each time step. Φ(T e ) has a simple and flexible analytical form, can describe all relevant interactions and is applicable for any kind of boundary conditions (bulk, thin films, clusters). Its overall shape is automatically adjusted by a self-learning procedure, which finally finds the global minimum in the parameter space. We show that Φ(T e ) can reproduce all thermal and nonthermal features provided by ab initio simulations. We apply the potential to simulate laser-excited Si nanoparticles and find critical damping of their breathing modes due to nonthermal melting. arXiv:1812.08595v1 [cond-mat.mtrl-sci]

Correction of Density-Functional-Theory based polynomial interatomic potentials to reproduce experimental melting properties

“…We construct the T e -dependent interatomic potential for Si [20] as a sum of a two-body potential Φ 2 , a three-body potential Φ 3 , an embedding function Φ ρ and the Helmholtz free energy of an isolated Si atom Φ 0 :…”

“…Femtosecond laser pules excite the electrons in matter to high electronic temperatures T e 's inducing significant ultrafast changes in the interatomic bonding whereas the ions remain mostly unaffected until electron-phonon interactions become active [12]. In order to address the short lived changes in interatomic bonding due to the hot electrons in large scale MD simulations, T e -dependent interatomic potentials were introduced [13][14][15][16][17][18][19][20], which depend beside the atomic coordinates also on the electronic temperature T e . The hot electrons cause many ultrafast phenomena like bond hardening or softening [21][22][23], structural solidsolid and solid-liquid phase transitions [24][25][26], phonon squeezing or antisqueezing [27,28], excitation of coherent phonons [29,30], which can be well described by T e -dependent density functional theory (DFT).…”

“…We recently developed a T e -dependent interatomic potential for Si [20] by fitting interatomic forces and structural energies from molecular dynamics simulations in thin-film geometry using T e -dependent DFT in the local density approximation. The obtained interatomic potential describes, when included with atomistic simulations, femtosecond laser-induced effects in Si, like the bond softening, thermal phonon antisqueezing, non-thermal melting, and ablation with remarkable accuracy.…”

Limitations of Structural Insight into Ultrafast Melting of Solid Materials with X-ray Diffraction Imaging

“…This induces atomic dynamics, which result in a transformation of the material structure. Experimentally, such transitions were first observed for materials irradiated with high-fluence lasers at near-infrared or visible wavelengths [1,[3][4][5][6][7][8][9][10]. Currently, freeelectron lasers (FELs) [11], emitting photons in the ultraviolet and X-ray range, can also generate pulses intense enough to trigger nonthermal melting in semiconductors after a single shot.…”

Damage processes in ruthenium thin films induced by ultrashort laser pulses

“…The obtained EAM potential does not depend on the electron temperature, i.e., a possible influence of the excited electronic system on the interatomic potential is not taken into account. Development of a temperature-dependent potential is challenging [98], and can be considered as a possible future improvement of our model.…”