Quantum Monte Carlo for activated reactions at solid surfaces: Time well spent on stretched bonds
Bibliographic record
Abstract
Many chemical reactions involve bond‐dissociation. This is also true for reactions at solid surfaces, in which the dissociation step is often limiting but facilitated in comparison to gas‐phase reaction channels. This work considers N 2 dissociation. The molecule is strongly bound and stretched geometries are chosen. Heterogeneous catalysis by copper is simulated. It was investigated in our previous work as it is in many ways a prototype metal presenting a close‐packed surface here. These nitrogen molecules are adsorbed on copper and fixed geometries on the dissociation reaction pathway for stretched N 2 are given using density functional theory (DFT) calculations in a plane‐wave basis. This dissociating molecule appears to be underbound using the ab initio Perdew, Burke, Ernzerhof (PBE) DFT functional but while this phenomenon accounts for a few percent at 5 Å, at 6 Å, PBE gives less than 30% of the binding energy. This indicates the onset of dissociation. The PBE wave‐functions at these bond‐lengths serve as trial input for Quantum Monte Carlo (QMC) simulations of the ground states to obtain highly accurate correlated results for the associated activation barriers indicating the catalytic effect on this dissociation. The geometries from this bond‐stretching study mimic the transition state (TS). This procedure requires no search for the actual TS geometry. Finite‐size effects and fixed‐node error are possible limitations to accuracy of this type of QMC study. We are able to limit fixed‐node error, using certain trial wave‐functions. The finite‐size effect is considerable, although comparing two adsorbed geometries cancels about 90% with respect to clean surfaces. Unfolding the cell to simulate a 9 k‐point grid (rather than a single k‐point) reduces the remainder by at least a factor 130 but relations for calibrating the remaining (2 mHa) error on converged grids are also used. The pseudopotential used to represent the atomic core of copper must also be determined carefully: we leave 11 active electrons but include the 3d shell in the pseudopotential. © 2014 Wiley Periodicals, Inc.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".