Density functional theory study of the relative stability of the iron disulfide polymorphs pyrite and marcasite

The performance of density functional theory has been widely examined with regard to its ability to predict the properties of minerals, though less attention has been given to the correct determination of the relative stability of structurally similar polymorphs. Here a detailed examination is performed of the numerical and theoretical factors that may influence the structure and relative energetics of two such polymorphs of iron disulfide, namely, pyrite and marcasite, within density functional theory. Both the local-density approximation and commonly used generalized gradient approximation exchange-correlation functionals, such as Perdew, Burke and Ernzerhof (PBE), are found to predict that marcasite is more stable than pyrite, at variance with experiment. Allowing for the zero-point energy of vibration fails to remedy this discrepancy. While inclusion of a sufficiently large Hubbard $U$ parameter for iron is found to reverse the stability, this comes at the expense of a very poor description of other properties. Examination of three generalized gradient approximations developed specifically for the solid state, namely, AM05, Wu-Cohen and PBEsol, demonstrates that all of these functionals offer a superior description of the structures and relative energies of pyrite and marcasite through correctly predicting that the former is the ground-state phase at ambient conditions.

密度泛函理论在预测矿物性质方面的表现已被广泛研究，然而对于结构相似的多晶型物相对稳定性的正确判定却关注较少。在此，我们在密度泛函理论框架内，对可能影响二硫化铁的两种这样的多晶型物（即黄铁矿和白铁矿）的结构和相对能量的数值和理论因素进行了详细研究。发现局域密度近似以及常用的广义梯度近似交换关联泛函，如佩德韦 - 伯克 - 厄恩泽霍夫（PBE），都预测白铁矿比黄铁矿更稳定，这与实验结果不符。考虑振动零点能也无法纠正这一差异。虽然发现对铁采用足够大的哈伯德$U$参数可扭转稳定性，但这是以对其他性质的描述非常差为代价的。对三种专门为固态开发的广义梯度近似（即AM05、吴 - 科恩和PBEsol）的研究表明，所有这些泛函都能通过正确预测黄铁矿在环境条件下是基态相，从而对黄铁矿和白铁矿的结构和相对能量给出更好的描述。