Extent of Spin Contamination Errors in DFT/Plane-wave Calculation of Surfaces: A Case of Au Atom Aggregation on a MgO Surface.

Kohei Tada,Tomohiro Maruyama,Mitsutaka Okumura,Shingo Tanaka,Hiroaki Koga

doi:10.3390/molecules24030505

Abstract

The aggregation of Au atoms onto a Au dimer (Au2) on a MgO (001) surface was calculated by restricted (spin-un-polarized) and unrestricted (spin-polarized) density functional theory calculations with a plane-wave basis and the approximate spin projection (AP) method. The unrestricted calculations included spin contamination errors of 0.0–0.1 eV, and the errors were removed using the AP method. The potential energy curves for the aggregation reaction estimated by the restricted and unrestricted calculations were different owing to the estimation of the open-shell structure by the unrestricted calculations. These results show the importance of the open-shell structure and correction of the spin contamination error for the calculation of small-cluster-aggregations and molecule dimerization on surfaces.

Highlights

Dimerization and its reverse process, homolytic cleavage, are basic chemical reactions, which are important for investigating heterogeneous reactions on surfaces [1,2,3,4,5,6,7,8,9,10,11,12]
In order to clarify the effects of spin contamination error and static correlation, the aggregation reaction of Au atoms (Au2 dissociation) on the MgO (001) surface have been investigated in detail
The calculation results show that the singlet state calculated by spin-polarized density functional theory (DFT) is the ground state throughout the reaction, and that the calculated energy is affected by the spin contamination error

Summary

Introduction

Dimerization and its reverse process, homolytic cleavage, are basic chemical reactions, which are important for investigating heterogeneous reactions on surfaces [1,2,3,4,5,6,7,8,9,10,11,12]. Dissociation of hydrogen on metal surfaces is an elementary reaction for hydrogenation by heterogeneous metal catalysts, and dimerization of nitrogen atoms and nitric monoxide (NO) molecules are regarded as elemental reactions for NOx elimination from exhaust gases. Both dissociation and dimerization of metal clusters on their support surfaces are crucial for clarifying the degradation mechanism of nanosized metal catalysts, especially gold catalysts [10,13,14,15,16,17,18]. We perform multi-reference calculations or spinpolarized (spin-unrestricted) calculations [19,20,21,22,23,24,25,26,27]

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Results

Conclusion