Benchmarking DFT surface energies with quantum Monte Carlo

Bulk and surface energetics of crystalline lithium hydride: Benchmarks from quantum Monte Carlo and quantum chemistry

“…The CCSDT and CCSDT(Q) calculations were performed using MRCC 35,36 as a module in Molpro and the diagonal Born-Oppenheimer correction (DBOC) calculations were performed using PSI3 37 . All other calculations were performed using Molpro LDA, PBE and rPBE functionals, these DFT results being taken from our earlier work 4 . The very close agreement between the DMC and QC results for σ confirms that both approaches give high accuracy, and shows that the results can be used as benchmarks for assessing DFT approximations.…”

“…In some cases, the variation of predicted σ values with the assumed exchange-correlation functional has been studied, and it is found that generalized gradient approximations (GGA) such as PBE and PW91 often give σ values that are ∼ 30 % lower than those predicted by the local density approximation (LDA). [2][3][4][5] Since GGAs are generally more accurate than LDA for bonding energies, and since the energy needed to form a surface would seem to be closely related to the energy needed to break bonds, it might be expected that GGA values of σ would be more accurate. However, in the few cases where there are reliable experimental data, this expectation is not fulfilled, and the rather scattered evidence suggests that the LDA may be more accurate.…”

“…In principle, electronic-structure methods based on density-functional theory (DFT) should be capable of giving reliable surface energies, but in practice it is found that computed values depend strongly on the approximation used for the exchange-correlation energy. [1][2][3][4] There are two main kinds of electronic-structure technique that allow one to go beyond DFT and achieve better accuracy: quantum Monte Carlo (QMC), and the wavefunction-based correlation techniques usually associated with molecular quantum chemistry (QC). We show here how these two very different approaches can be used in a complementary way to produce accurate benchmark values for surface formation energy, using as a test case the (001) surface of crystalline LiH.…”

The role of density functional theory methods in the prediction of nanostructured gas-adsorbent materials

“…For these reasons, we envisage that QMC methods will play an increasingly more relevant role in prospective DFT benchmark studies of GAM. (Actually, the DMC method has already been applied to the study of metal hydrides [228,229,287] and metal oxides [288][289][290], two important families of materials within the context of hydrogen storage and carbon capture.) It is worth noticing, however, that QMC methods are neither exempt of some important technical problems.…”

Ab initio statistical mechanics of surface adsorption and desorption. II. Nuclear quantum effects

“…Improvements are much needed, because DFT energetics of surface systems often depends significantly on the approximation used for exchange-correlation energy. Increasingly effective methods for applying highly-correlated quantum chemistry to extended systems [32,28,8,29,30,31], the growing power of quantum Monte Carlo techniques [38,39,40,41,42,9,43], and progress with improved van der Waals DFT functionals [44] give promising signs that ab initio calculations on surface adsorbates with chemical accuracy or better are now coming within reach. These improvements will enhance the importance of being able to account for nuclear quantum corrections.…”