Ab initio description of non-adiabatic effects in dissociative adsorption at surfaces

基于微观理解的预测性材料科学建模需要对原子尺度下所有基本过程的透彻了解。单个气相分子在金属表面的（解离）吸附是这样一个基本过程，对于涉及暴露于现实气体环境的表面的任何应用都至关重要，多相催化只是一个突出的例子。不幸的是，我们目前对这一基本过程的理解甚至对于最简单但普遍存在的双原子分子如O2非常浅。缺乏可靠的和解决的信息与表面电子结构的相互作用的碰撞分子（总结在一个所谓的势能面（PES）的形式），经验理论援引有争议的方案来解释实验上可访问的，积分动力学量，如在表面的粘附概率。在这些情况中，经常讨论的是非绝热效应在离解中的作用，即可能违反玻恩-奥本海默近似和电子分布，不能瞬时跟随核运动。对这一问题的清晰认识只能来自第一性原理理论，如密度泛函理论（DFT），它涉及对系统电子结构的可靠但近似的描述。完全基于绝热的DFT-PES，这样的理论在过去主要是为H2在金属表面的解离而开发的，其中非绝热效应显然不起作用。最近的方法发展，现在也使非绝热PES的计算约束DFT方法。相应地，我们提出了第一个系统的调查解决的真实的重要性的非绝热效应在02解离。为了明确地确定这些效应所起的作用，这需要同时解决许多其他尚未完全理解的问题，例如电子相关性描述所需的准确性或表面迁移率的影响。专注于O2在一组代表性表面上解离的动力学，预计周期表上出现的趋势图将有助于对这种最重要分子的（解离）吸附的第一次全面理解，这也可能对其他广泛存在的化合物如N2，NO或CO的解离提供一些指导。

A predictive materials science modeling based on microscopic understanding requires a thorough knowledge of all underlying elementary processes at the atomic scale. The (dissociative) adsorption of individual gas phase molecules at metal surfaces is such an elementary process that is of crucial relevance for any application involving surfaces exposed to realistic gas environments, with heterogeneous catalysis forming just one prominent example. Unfortunately, our present understanding of this fundamental process is even for a most simple, but ubiquitous diatomic molecule like 02 very shallow. Lacking reliable and resolved information about the interaction of an impinging molecule with the surface electronic structure (summarized in form of a socalled potential-energy surface (PES)), empirical theories have invoked controversial scenarios to account for experimentally accessible, integral kinetic quantities like the sticking probability at the surface. Among these scenarios is the frequently discussed role of non-adiabatic effects in the dissociation, i.e. a possible violation of the Born-Oppenheimer approximation and electron distributions that are not able to follow the nuclear motion instantaneously. Clarifying insight into this matter can only come from firstprinciples theories like density-functional theory (DFT), which involve a reliable, though approximate description of the electronic structure of the system. Based exclusively on the adiabatic DFT-PES, such theories have in the past been predominantly developed for H2 dissociation at metal surfaces, where non-adiabatic effects apparently play no role. Recent methodological developments have now also enabled the calculation of diabatic PESs within constrained DFT approaches. Correspondingly, we propose a first systematic investigation addressing the real importance of non-adiabatic effects in 02 dissociation. To unambiguously pin down the role played by these effects, this requires to concomitantly tackle a number of other, not yet fully understood issues like the required accuracy in the description of electron correlation or the influence of surface mobility. Focusing at the dynamics of 02 dissociation at a representative set of surfaces, the emerging trend picture over the periodic table is expected to contribute to a first comprehensive understanding of the (dissociative) adsorption of this most important molecule, that may also give some guidance on the dissociation of other widespread diatomics like N2, NO or CO.