A molecular dynamics study of bulk and shear viscosity of liquid iron using embedded-atom potential

Molecular dynamics simulations employing a many-body embedding potential model have been conducted to calculate both bulk and shear viscosity of pure liquid iron at the Earth's outer core conditions. Liquid iron shear viscosity thus obtained is in the order of 10⁻² Pa · s and is in close agreement with previous estimates. In contrast, liquid iron bulk viscosity is in the order of 10⁻³ to 10⁻⁴ Pa · s and is much smaller than previous estimates. Consequently, the ratio of bulk to shear viscosity is close to 0.1. This value disagrees with both the common speculation that bulk and shear viscosities are equal at ambient pressure, and the previous inference that bulk viscosity of liquid iron is much larger than shear viscosity at outer core conditions. Potential implications of present data are also briefly given for the dynamic state of the outer core. Received: 9 April 1999 / Revised, accepted: 7 June 1999