qchem-prescreen-xtb

Fast pre-DFT prescreening with GFN2-xTB via the xtb binary. Use to (1) pre-optimize geometries before DFT, (2) triage VAE/generative molecules that are likely to fail SCF/optimization, (3) run optional cheap frequency checks, and (4) produce standardized prescreen QC flags and artifacts for qchem-workflow batch pipelines.