Philipsen P H T, Baerends E J
Department of Chemistry, Section Theoretical Chemistry, Vrije Universiteit, Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
J Phys Chem B. 2006 Jun 29;110(25):12470-9. doi: 10.1021/jp060886e.
We present the result of a fragment-based energy decomposition analysis on some molecule-surface interactions. The analysis allows us to quantify the Pauli repulsion, its relief, and the attractive orbital interaction energy. In a metal, the existence of incompletely occupied energy bands causes significant relief of the Pauli repulsion due to escape of antibonding electrons to unoccupied states at the Fermi energy. This is the key electronic structure feature of metals that causes metal-molecule bond energies to be stronger and dissociation barriers of chemisorbed molecules to be much lower than those in comparable systems with no or one metal atom. As examples, we discuss the energy decomposition for the activated dissociation of hydrogen on the Cu surface and its unactivated dissociation on Pd, and for the (activated) chemisorption of N2 on W. We show that in all cases the relief of Pauli repulsion is of crucial importance for the chemisorption energy and for the low (or nonexistent) dissociation barriers. The barrier to the chemisorption well for nitrogen on tungsten is clearly related to a late relief of the Pauli repulsion. The relief of Pauli repulsion is important in lowering the barrier to dissociation of H2 on both Cu and Pd, but the difference in barrier heights for Cu and Pd appears to not be due to stronger relief of Pauli repulsion on Pd but primarily to the Pauli repulsion itself being stronger on Cu than on Pd, the relief energy being quite comparable on the two metals.
我们展示了基于片段的能量分解分析在一些分子 - 表面相互作用上的结果。该分析使我们能够量化泡利排斥、其缓解情况以及吸引性轨道相互作用能。在金属中，由于反键电子逃逸到费米能级的未占据态，未完全占据的能带的存在导致泡利排斥显著缓解。这是金属的关键电子结构特征，使得金属 - 分子键能更强，化学吸附分子的解离能垒比没有或只有一个金属原子的可比体系中的解离能垒低得多。作为例子，我们讨论了氢在铜表面的活化解离及其在钯上的非活化解离，以及氮在钨上的（活化）化学吸附的能量分解。我们表明，在所有情况下，泡利排斥的缓解对于化学吸附能和低（或不存在）解离能垒至关重要。氮在钨上化学吸附阱的能垒显然与泡利排斥的延迟缓解有关。泡利排斥的缓解对于降低氢在铜和钯上的解离能垒都很重要，但铜和钯的能垒高度差异似乎不是由于钯上泡利排斥的缓解更强，而是主要由于铜上的泡利排斥本身比钯上更强，两种金属的缓解能相当。
