Letter pubs.acs.org/JPCL
Surface Adsorption Energetics Studied with “Gold Standard” WaveFunction-Based Ab Initio Methods: Small-Molecule Binding to TiO2(110) Adam Kubas,†,§ Daniel Berger,‡ Harald Oberhofer,‡ Dimitrios Maganas,† Karsten Reuter,*,‡ and Frank Neese*,† †
Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34−36, 45470 Mülheim an der Ruhr, Germany Chair for Theoretical Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany
‡
S Supporting Information *
ABSTRACT: Coupled-cluster theory with single, double, and perturbative triple excitations (CCSD(T)) is widely considered to be the “gold standard” of ab initio quantum chemistry. Using the domain-based pair natural orbital local correlation concept (DLPNO-CCSD(T)), these calculations can be performed on systems with hundreds of atoms at an accuracy of ∼99.9% of the canonical CCSD(T) method. This allows for ab initio calculations providing reference adsorption energetics at solid surfaces with an accuracy approaching 1 kcal/mol. This is an invaluable asset, not least for the assessment of density functional theory (DFT) as the prevalent approach for large-scale production calculations in energy or catalysis applications. Here we use DLPNO-CCSD(T) with embedded cluster models to compute entire adsorbate potential energy surfaces for the binding of a set of prototypical closed-shell molecules (H2O, NH3, CH4, CH3OH, CO2) to the rutile TiO2(110) surface. The DLPNOCCSD(T) calculations show excellent agreement with available experimental data, even for the “infamous” challenge of correctly predicting the CO2 adsorption geometry. The numerical efficiency of the approach is within 1 order of magnitude of hybrid-level DFT calculations, hence blurring the borders between reference and production technique.
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Systematic benchmarking against accurate reference numbers is thus a critical element in the development and assessment of any DFT functional. For molecular systems, corresponding benchmarks against extensive thermochemical and kinetic databases are well established.10,11 The reference energetics in these databases are thereby drawn from either experiment or high-level ab initio wave-function-based calculations, foremost coupled cluster (CC) theory. Unlike DFT, the CC hierarchy systematically converges toward the exact solution of the Schrödinger equation. In particular, coupled-cluster theory with single, double, and perturbative triple excitations, CCSD(T), is the widely accepted “gold standard” method. At the basis limit it provides electronic energies with chemical accuracy (
