MolTUI

MolTUI is a terminal molecular and crystallographic viewer designed for quick inspection of geometries, trajectories, orbitals and normal modes directly in the terminal using Unicode characters. Ideal for remote SSH sessions and lightweight analyses.

Installation

pip install moltui
# or
uv tool install moltui

Usage

moltui <file>

Features

MolTUI is organized in a series of modes that can be cycled using the m (forward) and M (backward) keys. Each mode opens a respective sidebar which can be toggled on and off with S. The modes consist of molecular orbitals, normal modes and geometry and availability depends on the file format that was opened.

Visualize Orbitals

• The rendering of orbitals can be toggled via o.
• Molden and .gbw files can contain multiple molecular orbitals. Cycle through MOs with next and prev.

Analyze Geometry

• Bond lengths, angles and dihedrals can be viewed using the geometry key which opens a sidebar. Navigate between tabs via <tab>.
• The quantity is highlighted in yellow on the molecule.
• Sort the quantity in increasing magnitude via s.
• Atom indices can be toggled via #.

Periodic Systems

• Periodic systems can be provided using the extended XYZ and CIF file formats
• The toggling of the periodicity is achieved via the b key
• The rendering of the box can be toggled in the visual pane

Animations

Trajectories

Trajectories can be provided in the multi-XYZ file format (essentially multiple XYZ files concatenated together). Toggle a looping animation of the trajectory using <space> and cycle individual frames using [ and ]. The geometry sidebar values updates live with the current frame's geometry.

Normal Modes

Normal modes can be provided either via the Molden or Orca .hess file formats. Animation playing can be toggled with <space>.

Export to PNG Format

The e key exports the current scene to a PNG.

Tune Visuals

The V key opens a sidebar where the isovalue, molecule style and lighting can be modified.

The lower case v cycles between the styles.

CPK	Licorice	VDW

Toggle between light and dark mode with i.

Light	Dark

Supported formats

Format	Geometry	Trajectory	Orbitals	Normal Modes
XYZ / extXYZ	✓	✓	—	—
CIF	✓	—	—	—
Gaussian ZMAT	✓	—	—	—
Gaussian Cube	✓	—	✓	—
Molden	✓	—	✓	✓
Gaussian .fchk	✓	✓	✓	✓
Orca .GBW¹	✓	—	✓	—
Orca .hess	✓	—	—	✓
TrexIO²	✓	—	✓	—

✓ supported; — not part of the file format

¹ Requires orca_2mkl in PATH

² Requires installing moltui[trexio]

Quantum Chemistry Inputs

The molecular structures can be viewed from the inputs of the following programs

• Orca, Molcas, Q-Chem, Gaussian, NWChem, Turbomole, Molpro, MRCC, CFOUR, Psi4, GAMESS Jaguar

Keybindings

Navigation

Key	Action
h/j/k/l or arrows	Rotate left/down/up/right
,/.	Roll clockwise/counter-clockwise
J/K or +/-	Zoom out/in
t	Toggle pan/rotation mode
c	Center view
r	Reset view

Display

Key	Action
o	Toggle orbital isosurfaces
i	Toggle dark/light theme
B	Toggle bonds
b	Toggle periodicity
e	Export PNG
v	Toggle style (CPK, Licorice, VDW)
#	Toggle atom numbers

Panels

Key	Action
m / M	Cycle sidebar mode forward/backward (Geometry, MO, Normal Modes)
S	Toggle current sidebar (hide/show)
V	Toggle Visual settings panel
n/p	Next/previous row in the active sidebar table
d/u	Half page down/up in datatable
g/G	Top/bottom of the datatable

Geometry panel

Key	Action
Tab/Shift+Tab	Switch Bonds/Angles/Dihedrals tab
s	Toggle sort by value for active tab

Visual panel

Key	Action
n/p	Move focus to next/previous control
Tab/Shift+Tab	Increase/decrease focused slider, or cycle style option

Animation and modes

Key	Action
Space	Toggle play/pause trajectory or normal mode animation
[ / ]	Previous/next animation step (frame/phase)

General

Key	Action
q	Quit

Known Issues

• Only up to g-shells are implemented as this is the highest orbital shell officially supported by the Molden format.
• The content is rendered using braille Unicode characters and, therefore, the quality of rendering can depend on the font and terminal emulator. All figures in the repository have been generated using the JetBrains Mono Nerd Font in the Kitty terminal.
• The Orca GBW file format is typically incompatible between versions. Therefore, the orca_2mkl should ideally be of the same version as the Orca version used to produce the GBW file. Newer version of Orca can try to recover earlier GBW files using the rescue feature.

Acknowledgements

Parser tests are cross-validated with data and reference parsers from IODATA, cclib / cclib-data, PySCF, and ASE.