---
title: "Computational Chemistry Add-on: Open Gaussian and ORCA Files in Your Browser | MolDraw Blog"
url: https://www.moldraw.com/blog/computational-chemistry-plugin-gaussian-orca-viewer-guide.html
description: "How to use the free MolDraw Computational Chemistry add-on: open Gaussian, ORCA, GAMESS, xtb, Molden, cube and trajectory files, read key results, animate IR modes, draw orbitals, plot UV-Vis from TD-DFT, play scans and build new input files. Annotated screenshots for every step."
lang: en
publisher: Scidart Academy
generated: 2026-11-07
---
# Computational Chemistry Add-on: Open Gaussian and ORCA Files in Your Browser

Published: 7 Nov 2026 · Author: Scidart Academy · Reading time: ~9 min

![The MolDraw Computational Chemistry add-on: the HOMO of divinylbenzene drawn as red and blue lobes and an IR spectrum from a Gaussian frequency job](https://www.moldraw.com/blog/thumbs/compchem-plugin-guide.webp)

Molecular orbitals and an IR spectrum from Gaussian output, shown in the CompChem tab.

**Short answer:** Open the 3D viewer, press **+** and install **Computational Chemistry**. In the CompChem tab, drop a Gaussian, ORCA, GAMESS, xtb, Molden, cube or trajectory file (or open an example). You get the key results, IR/Raman and UV-Vis spectra you can export or copy as transparent images, animated normal modes, molecular orbitals, trajectories with energy profiles, and a builder for your next input file.

How to read the screenshots: each orange number in a picture matches the numbered note under it. Dashed boxes with a magnified panel are zoomed-in details.

## Step 1: Install the Computational Chemistry add-on

![The add-on menu that opens from the plus button next to the 3D viewer tabs, with Computational Chemistry highlighted](https://www.moldraw.com/blog/images/compchem/addon-menu-compchem.webp)

The **+** next to the 3D viewer tabs lists every add-on. Click **Install** next to Computational Chemistry.

1. The **+** button at the end of the tab row (Structure, Protein, …) opens the add-on menu.
2. **Computational Chemistry**: click **Install** and a **CompChem** tab appears.

1. Open the [MolDraw editor](https://www.moldraw.com/) and sign in. A free account is enough to use add-ons.
2. Open the 3D viewer on the right (the **3D** button at the bottom of the atom bar) and press **+** next to the tabs.
3. Click **Install** next to **Computational Chemistry** (callout 2). The **CompChem** tab opens, and the button changes to **Open**.

Add-ons stay installed on your account. To remove one, hover its tab and click the small **×**. You can also manage them under **Settings** › **Plugins**.

## Step 2: Open an output file or an example

![The CompChem start screen: a drop zone listing Gaussian, ORCA, GAMESS, xtb, Molden, XYZ and PDB trajectory and cube files, Open and New calculation buttons, and twelve example cards such as Divinylbenzene opt + freq, orbitals, TD-DFT and a dihedral scan](https://www.moldraw.com/blog/images/compchem/cc-home.webp)

The start screen: drop your files, or try one of twelve examples.

1. **Drop zone.** Drag files here or click to choose them. Several files open as tabs; files from one job (for example `.log` + `.fchk`, or `.out` + `.gbw`) open together in one tab.
2. **Try an example**: real outputs to explore before you use your own.
3. Each card names the program and file type (here a Gaussian `.log` with an optimisation and a frequency job).
4. **Open** (folder icon) and **New calculation**, which builds input files (Step 8).

| Gaussian | `.log` / `.out` (including `--Link1--` multi-job files) and formatted checkpoint `.fchk`. |
| --- | --- |
| ORCA | `.out` (orbitals with PrintMOs), binary `.gbw` and `.molden.input`. |
| GAMESS (US) | `.log`, including Hessians and transition states. |
| xtb | Output plus `xtbopt.log` for the optimisation path. |
| Molden | Geometry, basis and orbitals (including d and f functions). |
| Trajectories | Multi-frame XYZ (energies from the comment lines) and multi-model PDB. |
| Volumes | Gaussian cube files with ± isosurfaces. |

Files are read in your browser. Nothing is uploaded to a server.

## Step 3: Read the key results (Summary)

We opened the example **Divinylbenzene opt + freq** (a B3LYP/STO-3G optimisation followed by a frequency job).

![The Summary tab for dvb_opt_freq_link1.log: file tab, 3D toolbar, the optimised divinylbenzene molecule, the Summary, Orbitals, Vibrations and Trajectory tabs, a green normal termination notice and a key results table with energy, model, charge, HOMO/LUMO, gap, dipole moment, optimisation steps, vibrational modes and atoms](https://www.moldraw.com/blog/images/compchem/cc-summary.webp)

Summary collects the numbers you would otherwise search the log for.

1. **File tab.** Each open file gets a tab; the **+** on the right opens more.
2. **3D toolbar**: open, new calculation, fit view, spin, display style, atom labels, measure, add to canvas, send as a 2D drawing, copy image and export.
3. **3D view** of the final geometry. Drag to rotate, scroll to zoom.
4. **Result tabs.** Only the tabs your file has data for appear: Summary, Orbitals, Vibrations, UV-Vis, Trajectory.
5. **Status**: normal termination, or the warnings and errors found in the file.
6. **Key results**: final energy (−382.30826660 Eh), method and basis, charge and multiplicity, HOMO/LUMO and gap, dipole moment, optimisation steps, number of modes and atoms. The copy icons copy single values.

![Further down Summary: the optimisation convergence plot of ΔE against step for five steps, a note that energies are relative to the lowest, and the thermochemistry table at 298.15 K and 1 atm with zero-point energy, thermal corrections to E, H and G and T·S in Eh and kcal/mol](https://www.moldraw.com/blog/images/compchem/cc-convergence.webp)

Further down Summary: convergence and thermochemistry.

1. **Convergence** of the optimisation (switch between Geometry and SCF). Click a point to open that step.
2. Energies are relative to the lowest one, which is given in Eh.
3. **Thermochemistry** at the temperature and pressure of the job: zero-point energy, thermal corrections to E, H and G, and T·S, in Eh and kcal/mol.

## Step 4: Look at the IR spectrum and animate normal modes

![The Vibrations tab: the molecule with orange displacement arrows for the selected mode, the IR spectrum from 4000 to 0 cm−1 with bold axes, export and copy buttons, line shape, FWHM and scale factor controls and the selected mode 45 at 3396.4 cm−1 with amplitude and speed](https://www.moldraw.com/blog/images/compchem/cc-vibrations.webp)

Click a peak to animate that vibration in 3D.

1. The selected mode, animated, with arrows showing which way each atom moves.
2. The **Vibrations** tab.
3. The broadened **IR spectrum**. Click a peak or a stick to select its mode. When the file has Raman activities, an IR/Raman switch appears.
4. **Export** as CSV (curve and sticks), SVG or PNG, and **Copy image** (see the tip below).
5. **Line shape**: Lorentzian or Gaussian.
6. **FWHM**: the peak width in cm⁻¹.
7. **Scale factor** for the frequencies (for example 0.96 to 0.98 for hybrid DFT).
8. The selected mode (here 45 at 3396.4 cm⁻¹, a C-H stretch). Below it: amplitude, speed and pause.

**Tip for slides:** the **Copy image** button (the last icon above the spectrum) puts the plot on your clipboard as a high-resolution PNG with a transparent background. Paste it straight into PowerPoint, Keynote or Google Slides; no file to save. The axes, numbers and labels are drawn bold so they stay readable on a projector.

## Step 5: Draw molecular orbitals

Orbitals need the basis set and MO coefficients, so open a `.fchk`, `.gbw`, Molden file or an ORCA output with PrintMOs. We used the example **Divinylbenzene orbitals** (`.fchk`).

![The Orbitals tab for divinylbenzene: the HOMO drawn as red and blue lobes over the π system, HOMO −4.166 eV, LUMO 1.018 eV and gap 5.184 eV, the Surface choice between Total density and HOMO, isovalue and opacity sliders, the grid quality switch and the table of 60 orbitals](https://www.moldraw.com/blog/images/compchem/cc-orbitals.webp)

The π HOMO of divinylbenzene: blue and red are the two phases of the wavefunction.

1. The orbital surface on the molecule: blue for positive, red for negative.
2. Frontier orbitals: **HOMO**, **LUMO** and **gap**, in eV or Eh.
3. **Surface**: total electron density or the selected orbital.
4. **Isovalue**: smaller values give bigger lobes.
5. **Opacity** of the surface.
6. **Grid**: Fast, Medium or Fine. Fine gives smoother surfaces and takes longer.
7. The **orbital table** (here 60 orbitals) with symmetry, occupation and energy. Click any row to draw that orbital.

Under the grid line the panel checks that the orbitals are orthonormal, so you know the file was read correctly.

## Step 6: Plot a UV-Vis spectrum from TD-DFT

![The UV-Vis tab for a TD-DFT output: a broadened absorption spectrum in nm with ε on the left axis and oscillator strength sticks on the right axis, bold axes, line shape and FWHM controls, a note naming the strongest transition S2 at 230.7 nm with f = 0.6779, the excited states table and the Copy image button](https://www.moldraw.com/blog/images/compchem/cc-uvvis.webp)

Five excited states of divinylbenzene, broadened into a spectrum.

1. The spectrum: ε (L mol⁻¹ cm⁻¹) against wavelength in nm, with each transition as a stick.
2. The right axis gives the **oscillator strength f** of the sticks. Dark (forbidden) states are dashed.
3. **Line shape** and **FWHM** (in eV).
4. The strongest transition, here S2 at 230.7 nm with f = 0.6779.
5. **Excited states** table: energy, wavelength, f and the main orbital transitions.
6. **Copy image**: a transparent PNG for your slides. CSV, SVG and PNG export sit next to it.

## Step 7: Play a scan or an optimisation

Multi-frame files play like a film. The example **Vinyl dihedral scan** is a 13-point relaxed scan of one vinyl group.

![The Trajectory tab for a 13-frame dihedral scan: the molecule at frame 4 with the vinyl group twisted, player controls, the frame description with ΔE 5.472 kcal/mol, speed and align options and the energy profile with two barriers, the clicked point at step 4 highlighted](https://www.moldraw.com/blog/images/compchem/cc-scan.webp)

Click a point on the energy profile to jump to that geometry.

1. The geometry of the current frame: at step 4 the vinyl group is twisted out of the ring plane.
2. Player: first, previous, play, next, last and loop.
3. The frame in words, with its energy and ΔE.
4. **Energy profile**, relative to the lowest frame. Two barriers show the vinyl group passing the perpendicular position twice.
5. The clicked point: frame 4, the top of the barrier at 5.472 kcal/mol.

## Step 8: Make an input file for your next calculation

Click **New calculation** (flask icon). It takes the geometry from the open file or from your 2D drawing.

![The New calculation panel: geometry from the open file or from the canvas, charge 0 and multiplicity 1 with 70 electrons singlet, and recipe cards for Opt + Freq, Single point, TS search, IRC, Scan, UV-Vis (TD-DFT), NMR and Conformers](https://www.moldraw.com/blog/images/compchem/cc-newcalc.webp)

Pick the geometry, the charge and a recipe.

1. **Geometry** from the open file or from the canvas.
2. **Charge** and **multiplicity**, with an electron count check.
3. **Recipe**: Opt + Freq, Single point, TS search, IRC, Scan, UV-Vis (TD-DFT), NMR or Conformers.
4. **Level of theory** (next picture).

![The input part of New calculation: preset B3LYP-D3(BJ)/def2-SVP, an Advanced link for method, basis, dispersion, solvent and resources, program buttons for Gaussian, ORCA, Psi4, xtb/CREST, MOPAC, GAMESS (US), NWChem and Q-Chem, and the generated Gaussian input dvb_dihedral_scan.gjf with copy and download buttons](https://www.moldraw.com/blog/images/compchem/cc-input.webp)

The ready-to-run input. Switch the program and the file is rewritten.

1. **Preset** level of theory, here B3LYP-D3(BJ)/def2-SVP.
2. **Advanced**: method, basis, dispersion, solvent and resources (cores, memory).
3. **Program**: Gaussian, ORCA, Psi4, xtb/CREST, MOPAC, GAMESS (US), NWChem or Q-Chem. Programs that cannot run the chosen recipe are crossed out.
4. Copy the input, download it, or download it with a run script.
5. The generated input file with the route line, charge, multiplicity and coordinates.

When the job finishes, drop its output back on the panel to see the results.

## Ways to use it

- **Checking a job:** see at a glance if it terminated normally, converged and has no imaginary frequencies.
- **Teaching:** animate normal modes, compare HOMO and LUMO, or play a torsion scan in class.
- **Papers and talks:** copy IR and UV-Vis plots as transparent images for slides, or export SVG for figures.
- **Next step:** build the next input from the result without retyping coordinates.

For predicted spectra without running a calculation, see the [Spectroscopy plugin](https://www.moldraw.com/blog/ai-spectroscopy-plugin-nmr-ms-uv-prediction.html) and the [IR spectrum viewer](https://www.moldraw.com/blog/ir-spectrum-viewer-guide.html).

## Questions and answers

### How do I open a Gaussian log file online?

Install the free Computational Chemistry add-on in MolDraw, open the CompChem tab and drop your .log or .out file on it. The file is read in your browser and is not uploaded.

### Which programs and files are supported?

Gaussian .log, .out and .fchk; ORCA .out, .gbw and .molden.input; GAMESS (US) .log; xtb output with xtbopt.log; Molden files; multi-frame XYZ and multi-model PDB trajectories; and cube files.

### How do I copy a spectrum into PowerPoint?

Click the Copy image button above the IR, Raman or UV-Vis plot. The plot goes to your clipboard as a high-resolution PNG with a transparent background; paste it into your slide.

### Can I see molecular orbitals?

Yes, when the file has the basis set and MO coefficients: Gaussian .fchk, ORCA .gbw, Molden files or ORCA output with PrintMOs. Pick any orbital from the table and set the isovalue.

### Can it write input files?

Yes. New calculation builds inputs for Gaussian, ORCA, Psi4, GAMESS (US), NWChem, Q-Chem, xtb/CREST and MOPAC from the open file or your drawing, for optimisations, frequencies, TS searches, IRC, scans, TD-DFT, NMR and conformer searches.

### Is the Computational Chemistry add-on free?

Yes. You only need a free MolDraw account to install add-ons.

## Related guides

[Symmetry plugin](https://www.moldraw.com/blog/symmetry-plugin-point-groups-3d.html) [Electrostatic potential maps](https://www.moldraw.com/blog/mep-plugin-electrostatic-potential-map.html) [All plugins](https://www.moldraw.com/docs/plugins/moldraw-plugins-overview-and-how-to-install/)

Last updated: November 7, 2026