LOBSTER's cobiBetween ... orbitalwise directive computes the crystal orbital bond index (COBI) for a chain of three or more atoms, broken down per orbital combination across the chain (e.g. p-p-p, or individual p_x-p_y-p_z combinations) rather than only as a single summed value. This is standard, already-published LOBSTER functionality (COBI itself, and its N-center/orbitalwise decomposition) — this page documents betapy's tooling for browsing that data, not a new analysis method.

This tooling is independent of the multicenter bond detector: it works from any LOBSTER directory containing NcICOBILIST.lobster, whether the cobiBetween directives that produced it came from betapy's own detector, from LOBSTER's cobiBetween ... orbitalwise output directly, or were written by hand.

This tooling defaults to NcICOBILIST.lobster's own integrated "Nc-ICOBI (at) eF" values rather than COBICAR.lobster's energy-resolved curves. There is a known LOBSTER issue related to cell translated interactions that can yield erroneous values.

LOBSTER writes an automatic Nc-ICOBI entry for every ordinary nearest-neighbour pair regardless of any cobiBetween directive, and because of periodicity most bonds naturally appear at more than one translation — so the same physical bond can almost always be cross-checked against itself directly in the file that's loaded. betapy.core.lobster.check_ncicobi_consistency does this automatically for every directory the GUI opens, grouping pairwise entries by (species pair, real-space distance) and reporting the spread of values within each group. A large spread there (versus the small, sub-percent scatter we'd expect from ordinary numerical noise) suggests this specific directory's NcICOBILIST may show the same kind of translation-dependent divergence we observed in COBICAR, and its multicenter values should then be treated with the same caution — not trusted just because they came from a different file. The result is shown as a banner at the top of the GUI tab; treat that banner, not simply the presence of NcICOBILIST.lobster, as the basis for how much to trust the numbers.

Two ways to get a reliable energy-resolved curve out of a translated chain, if you need one:

• Re-run LOBSTER on a supercell built large enough that the chain's atoms are genuinely distinct atom indices rather than periodic images of each other — a chain that needs a cell 0 -1 1-type translation in the conventional cell needs the supercell expanded (at least doubled) along whichever axis/axes that translation vector has a nonzero component in, not necessarily all three. Reduce KPOINTS roughly in proportion along each expanded direction to keep the same real-space k-sampling density. Once every atom in the cobiBetween directive sits at cell [0,0,0], the divergence we observed for translated interactions no longer applies.
• The "Use COBICAR energy-resolved curves" checkbox, off by default — see the GUI section below.

A LOBSTER directory containing:

• POSCAR (or POSCAR.lobster / POSCAR.lobster.vasp) — for atom-index mapping
• NcICOBILIST.lobster — produced whenever the lobsterin file contains one or more cobiBetween directives (3+ atoms); only chains requested with the orbitalwise flag carry the per-orbital breakdown, e.g.:

cobiBetween atom 1 atom 6 atom 8 orbitalwise

Directive syntax. LOBSTER's official cobiBetween syntax writes atom and its POSCAR index as separate tokens (atom 1, not atom1). betapy's multicenter detector writes directives in this official form; the parser also tolerates the concatenated form (atom1) for older files, but it is not the format LOBSTER itself expects.

Open the LOBSTER COBI tab from the "+" menu (top right of the tab bar). This tab does not depend on any phonon force-constant data — only a LOBSTER directory.

1. Open LOBSTER directory… — select a directory with NcICOBILIST.lobster. A banner appears immediately with the automatic reliability check result for this directory (see above) — read it before trusting anything below it. Every multicenter (3+ atom) chain found in the file is listed underneath, with its integrated ICOBI(N), orbital-row count (or "no orbitalwise data" if that chain wasn't requested with the orbitalwise flag), and a [cell-free] tag if the chain involves no periodic-cell translation — i.e. the one case where COBICAR energy-resolved values are also trustworthy, independent of the banner's verdict. Plain 2-atom entries are excluded from the chain list itself — LOBSTER writes an Nc-ICOBI row for every ordinary nearest-neighbour pair too (that's what the reliability check uses), but those pairwise values are already covered by the existing pairwise LOBSTER integration elsewhere in the app.
2. Select a chain to load its breakdown into the middle panel and the chart on the right, and to highlight its atoms (gold spheres, connected by gold bonds) in the 3D view on the far right. This view always shows the base LOBSTER unit cell (from the same POSCAR used for atom mapping), outlined by a light boundary box — never a phonon supercell, even if one happens to be loaded elsewhere in the app. A chain spanning a periodic-cell translation is drawn at its true, unwrapped geometry, so atoms outside the outlined cell are genuine "ghost" images the interaction actually reaches, not an artifact. Show cell boundary (in the 3D panel's side controls) toggles the box.
3. Use COBICAR energy-resolved curves (off by default) switches the data source and the chart from an integrated-value bar chart to an energy-resolved curve overlay, as described above. If the selected chain involves a translation, a warning banner appears above the chart — the checkbox doesn't block you from looking, it just flags that this is exactly the situation where we've seen COBICAR and NcICOBILIST disagree, so it's worth a second look before relying on the number. If COBICAR.lobster has no matching entry for the chain, it falls back to the NcICOBILIST bar chart automatically.
4. Group by orbital type (s/p/d/f) (default on) collapses individual m-resolved rows (5p_x, 5p_y, 5p_z, …) into coarse type sums — a 3-center chain with an s/p/d basis (9 orbitals/atom) has 729 individual rows but only 27 type-combinations. Uncheck to browse the full m-resolved list.
5. Hide |ICOBI| < unlists orbital contributions with nothing going on; 0 (default) shows everything.
6. Bar-chart mode (default): shows the total (top bar, black) plus every currently shown orbital row, sorted by |ICOBI(N)|, coloured by sign (blue = bonding/positive, red = antibonding/negative — same convention as the pairwise LOBSTER viewer). Clicking a row in the list outlines the matching bar. Curve mode (COBICAR checkbox on): select one or more rows in the list to overlay their energy-resolved curves with the total. Either way, Export plot… saves the chart as SVG/PDF/PNG, Export CSV… saves the currently shown rows (respecting the active grouping/threshold/data source) as a table of ICOBI(N) at the Fermi level.
7. Show gridlines toggles the dotted value-axis gridlines.
8. Lock aspect ratio for export forces the saved plot to a fixed narrow portrait shape (width : height = 1 : 1.618, the golden ratio) regardless of the panel's on-screen shape — only the exported file is affected, not the live preview. Leave unchecked to export whatever shape the panel currently is.

A near-zero total does not mean nothing is happening. Opposite-sign orbital contributions can cancel almost exactly in the sum even when individual orbital contributions are large — always check the orbital breakdown, not just the total, before concluding an interaction is negligible.

• The value axis is symmetric about zero, so bonding and antibonding character get equal visual weight regardless of which happens to be larger in magnitude. This convention also applies to betapy's other COHP/COOP/COBI curve plots (the pairwise LOBSTER viewer and the multicenter Nc-COBI popup), which — unlike this tab — do still read energy-resolved curves from *CAR.lobster; keep the caveat above in mind if any bond you inspect there involves a periodic-cell translation.

Plots exported to SVG or PDF (from this tab's Export plot… button) keep text as editable text objects rather than outlined shapes, so labels and axis text open as live, selectable text in Illustrator (or any other vector editor) — not paths you'd have to redraw. This applies regardless of whether Lock aspect ratio for export is checked.