Simulating the structure of amorphous Si0.5C0.5 using Lin–Harris molecular dynamics

Abstract

We have amorphised Si0.5C0.5 by ab initio generating random networks with the experimental density of 2.75 g/cm3. Two types of crystalline supercells were used at the start: one was a diamond-like periodic supercell of 64 atoms, containing 32 carbons and 32 silicons, chemically ordered, amorphised using Fast Structure®, and the other was an fcc crystalline periodic supercell with 108 atoms, 54 carbons and 54 silicons, chemically ordered, amorphised using DMol3 from the suite in Materials Studio 3.2®. The amorphisation is made by heating the periodic samples to just below the melting point (the undermelt–quench approach), and then cooling them down to 0 K. Then the structures are relaxed by annealing and quenching, and finally a geometry relaxation is carried out. Our simulations show that Cerius2 ® and Materials Studio 3.2 give equivalent results in general: atoms of one kind are almost completely surrounded by the atoms of the other kind. We also find that the two codes lead to total and partial radial distribution functions such that after weighting them with the corresponding experimental structure factors yield curves that are similar and comparable with experiment. Also C–C bonds with an average bond length of 1.35 Å are found.