Map how a system's energy changes as bonds, angles, or dihedrals vary. At each sampled point, Rowan holds the selected coordinates fixed and optimizes the remaining geometry. The results include optimized structures and a 1D energy profile or 2D energy surface, useful for exploring conformational changes and candidate reaction barriers.
Settings
Level of theory: choose the calculation method under "Level of theory" and the optimization accuracy under "Geometry optimization mode."
Coordinate: select "Bond," "Angle," or "Dihedral" under "Type," using 2, 3, or 4 atoms respectively. Enter atom indices starting at 1 or select atoms in the viewer; atom order matters for angles and dihedrals.
Range and sampling: "Start," "Stop," and "Num steps" define evenly spaced points, including both endpoints. Bond lengths use Å; angles and dihedrals use degrees. For example, 1–2 Å with 5 points samples 1, 1.25, 1.5, 1.75, and 2 Å.
Dimensions: "Add coordinate" makes coordinates change together within a dimension, with a shared point count. "Add second scan dimension" creates a 2D grid: 10 points in each dimension give 100 grid points.
Wavefront propagation: "Wavefront propagation?" is enabled by default. It revisits points using neighboring optimized structures to reduce dependence on scan direction and starting geometry, at additional computational cost.
Constraints: optionally freeze other coordinates; avoid constraining the same coordinate you are scanning.
Periodic systems: "Optimize cell?" allows the cell to relax when supported by the selected method.
Notes
The wavefront propagation approach can improve a scan but does not guarantee the global minimum at every point. Inspect optimized geometries and point convergence alongside the energy profile. A scan maximum is a candidate barrier, not a confirmed transition state; refine a promising structure with a transition-state optimization and check its vibrational modes.