Accurate path-integral molecular dynamics calculation of aluminum with improved empirical ionic potentials

Abstract

We show that an accurate description of the interplay between the anharmonic ionic interaction and the zero-point fluctuation of ions in crystalline aluminum (Al) can be achieved using the path-integral molecular dynamics (PIMD) method in conjunction with improved empirical modified embedded-atom method (MEAM) potentials. Our results show that the zero-point fluctuation of ions is noticeable at a temperature between 200 K and 250 K, roughly half of the Al Debye temperature of 428 K, with a selective influence on mechanical properties. The effect provides appreciable corrections to the lattice constant $a$, bulk modulus $B$, and elastic constant ${C}_{11}$ at low temperature, but without much influence on elastic constants ${C}_{12}$ and ${C}_{44}$. With a revised MEAM potential which takes into consideration the influence of zero-point fluctuations, the PIMD method has a much improved accuracy in $a, B$, and the $C$'s up to 700 K, when compared with precision experimental measurements. The largest errors of $a$ and $B$ can even be reduced by about an order in percentage below 300 K.