We propose a general strategy to develop accurate Force Fields (FF) for metallic systems derived from ab initio quantum mechanical (QM) calculations; we illustrate this approach for tantalum. As input data to the FF we use the linearized augmented plane wave method (LAPW) with the generalized gradient approximation (GGA) to calculate: (i) the zero temperature equation of state (EOS) of Ta for bcc, fcc, and hcp crystal structures for pressures up to ~500 GPa. (ii) Elastic constants. (iii) We use a mixed-basis pseudopotential code to calculate volume relaxed vacancy formation energy also as a function of pressure. In developing the Ta FF we also use previous QM calculations of: (iv) the equation of state for the A15 structure. (v) the surface energy bcc (100). (vi) energetics for shear twinning of the bcc crystal. We find that withappropriate parameters an embedded atom model force field (denoted as qEAM FF) is able to reproduce all this QM data. Thus, the same FF describes with good accuracy the bcc, fcc, hcp and A15 phases of Ta for pressures from ~ -10 GPa to \~ 500 GPa, while also describing the vacancy, surface energy, and shear transformations. The ability of this single FF to describe such a range of systems with a variety of coordinations suggests that it would be accurate for describing defects such as dislocations, grain boundaries, etc. We illustrate the use of the qEAM FF with molecular dynamics to calculate such finite temperature properties as the melting curve up to 300 GPa; we obtain a zero pressure melting temperature of T_{melt}=3150 +/- 50 K in good agreement with experiment (3213-3287 K). We also report on the thermal expansion of Ta in a wide temperature range; our calculated thermal expansivity agrees well with experimental data.
翻译:我们提出一个总体战略,为来自ABITIO 量子机械(QM)计算出来的金属系统开发准确的Force Fields(FF) 。 我们演示了对钽的这一方法。 作为向FF输入的数据,我们用通用梯度近似(GGA)计算:(一) Ta的状态零温度方程式(EOS)为 bcc、 fcc 和hcp 晶体进行压力到~500 GPa。 (二) 精度常数 。 (三) 我们使用混合基底假基代码来计算数量松散的空缺形成能量,作为压力的函数。在开发TaFF 时,我们还使用线性加速增强的平面波波波波波波(LAPW)计算:(四) A15结构的状态方程式。 (五) 表面能量 bcc (100) 。 (六) 螺旋结于 bcc 晶体。 (六) 我们发现,有了适当的参数, 我们的原子模型字段(deed qema) 和直径直径直径阵列的电场。