TY  - JOUR
A1  - Heiden, Sophia
A1  - Usvyat, Denis
A1  - Saalfrank, Peter
T1  - Theoretical Surface Science Beyond Gradient-Corrected Density Functional Theory
BT  - Water at alpha-Al2O3(0001) as a Case Study
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - The quantum chemical description of the adsorption, vibrations, and reactions of molecules at periodic solid surfaces is frequently based on a methodological "standard model": density functional theory (DFT) in the generalized gradient approximation (GGA), using plane wave bases and three-dimensional supercells. Although the computationally efficient GGA functionals can be very successful, cases are known where they do not perform so well. Most importantly, activation energies for chemical reactions are typically underestimated, with the consequence of computed reaction rates being too large. In this work, we consider a well-studied model system: water or water fragments adsorbed on an Al-terminated alpha-Al2O3(0001) surface as a test bed for studying the performance of electronic structure methods, both from DFT and wave function theory. On the DFT side, we employ two GGA exchange correlation functionals: PW91 and PBE with and without dispersion corrections, whose results are then compared to those of hybrid functionals B3LYP and HSE06. Further, we follow a periodic wave function approach in the form of local second-order Moller-Plesset perturbation theory, LMP2, on a Hartree-Fock reference. En route, we address issues arising from the choice of the basis set. The key findings of our study are as follows: (i) DFT-GGA adsorption energies are in reasonable agreement with both hybrid-DFT and LMP2 values. In particular, the deviations between the relative energies, corresponding to different adsorption structures, are in the range of the error due to missing dispersion corrections or the basis set error. (ii) Harmonic DFT-GGA vibrational frequencies for oxygen hydrogen stretch modes are by several tens of wavenumbers red-shifted compared to corresponding hybrid-DFT values. The latter are in much better agreement with recent experimental data. (iii) The activation energy for a hydrogen diffusion reaction is grossly underestimated by GGA compared to hybrid-DFT or LMP2, which in turn are quite comparable.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpcc.9b00407
SN  - 1932-7447
VL  - 123
IS  - 11
SP  - 6675
EP  - 6684
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Mullan, Thomas
A1  - Maschio, Lorenzo
A1  - Saalfrank, Peter
A1  - Usvyat, Denis
T1  - Reaction barriers on non-conducting surfaces beyond periodic local MP2
BT  - Diffusion of hydrogen on alpha-Al2O3 (0001) as a test case
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - The quest for "chemical accuracy" is becoming more and more demanded in the field of structure and kinetics of molecules at solid surfaces. In this paper, as an example, we focus on the barrier for hydrogen diffusion on a alpha-Al2O3 (0001) surface, aiming for a couple cluster singles, doubles, and perturbative triples [CCSD(T)]-level benchmark. We employ the density functional theory (DFT) optimized minimum and transition state structures reported by Heiden, Usvyat, and Saalfrank [J. Phys. Chem. C 123, 6675 (2019)]. The barrier is first evaluated at the periodic Hartree-Fock and local Moller-Plesset second-order perturbation (MP2) level of theory. The possible sources of errors are then analyzed, which includes basis set incompleteness error, frozen core, density fitting, local approximation errors, as well as the MP2 method error. Using periodic and embedded fragment models, corrections to these errors are evaluated. In particular, two corrections are found to be non-negligible (both from the chemical accuracy perspective and at the scale of the barrier value of 0.72 eV): the correction to the frozen core-approximation of 0.06 eV and the CCSD(T) correction of 0.07 eV. Our correlated wave function results are compared to barriers obtained from DFT. Among the tested DFT functionals, the best performing for this barrier is B3LYP-D3.
Y1  - 2022
U6  - https://doi.org/10.1063/5.0082805
SN  - 0021-9606
SN  - 1089-7690
VL  - 156
IS  - 7
PB  - AIP Publishing
CY  - Melville
ER  -