Max-Planck-Institut für Eisenforschung GmbH, D-40237, Düsseldorf, Germany.
J Phys Condens Matter. 2013 Oct 23;25(42):425401. doi: 10.1088/0953-8984/25/42/425401. Epub 2013 Sep 24.
As chromium is a decisive ingredient for stainless steels, a reliable understanding of its thermodynamic properties is indispensable. Parameter-free first-principles methods have nowadays evolved to a state allowing such thermodynamic predictions. For materials such as Cr, however, the inclusion of magnetic entropy and higher order contributions such as anharmonic entropy is still a formidable task. Employing state-of-the-art ab initio molecular dynamics simulations and statistical concepts, we compute a set of thermodynamic properties based on quasiharmonic, anharmonic, electronic and magnetic free energy contributions from first principles. The magnetic contribution is modeled by an effective nearest-neighbor Heisenberg model, which itself is solved numerically exactly by means of a quantum Monte Carlo method. We investigate two different scenarios: a weak magnetic coupling scenario for Cr, as usually presumed in empirical thermodynamic models, turns out to be in clear disagreement with experimental observations. We show that instead a mixed Hamiltonian including weak and strong magnetic coupling provides a consistent picture with good agreement to experimental thermodynamic data.
由于铬是不锈钢的决定性成分，因此对其热力学性质的可靠理解是必不可少的。如今，无参数的第一性原理方法已经发展到可以进行这种热力学预测的状态。然而，对于铬等材料，包括磁熵和更高阶的贡献，如非谐熵，仍然是一项艰巨的任务。我们采用最先进的第一性原理分子动力学模拟和统计概念，根据准谐、非谐、电子和磁自由能贡献计算了一组热力学性质。磁贡献通过有效近邻海森堡模型来建模，该模型本身通过量子蒙特卡罗方法进行数值精确求解。我们研究了两种不同的情况：对于通常假定在经验热力学模型中的铬的弱磁耦合情况，与实验观察结果明显不一致。我们表明，相反，包括弱磁和强磁耦合的混合哈密顿量提供了与实验热力学数据一致的一致图景。
