8.6.3. Using the LAMMPS GUI

This document describes LAMMPS GUI version 1.5.

LAMMPS GUI is a graphical text editor customized for editing LAMMPS input files that is linked to the LAMMPS library and thus can run LAMMPS directly using the contents of the editor’s text buffer as input. It can retrieve and display information from LAMMPS while it is running, display visualizations created with the dump image command, and is adapted specifically for editing LAMMPS input files through text completion and reformatting, and linking to the online LAMMPS documentation for known LAMMPS commands and styles.


Pre-compiled, ready-to-use LAMMPS GUI executables for Linux (Ubuntu 20.04LTS or later and compatible), macOS (version 11 aka Big Sur or later), and Windows (version 10 or later) are available for download. They may be linked to a development version of LAMMPS in case they need features not yet available in a released version. Serial LAMMPS executables of the same LAMMPS version are included as well. The source code for the LAMMPS GUI is included in the LAMMPS source code and can be found in the tools/lammps-gui folder. It can be compiled alongside LAMMPS when compiling with CMake.

LAMMPS GUI tries to provide an experience similar to what people traditionally would do to run LAMMPS using a command line window:

  • editing inputs with a text editor

  • run LAMMPS on the input with selected command line flags

  • and then use or extract data from the created files and visualize it

That procedure is quite effective for people proficient in using the command line, as that allows them to use tools for the individual steps which they are most comfortable with. It is often required when running LAMMPS on high-performance computing facilities.

The main benefit of using the LAMMPS GUI application instead is that many basic tasks can be done directly from the GUI without switching to a text console window or using external programs, let alone writing scripts to extract data from the generated output. It also integrates well with graphical desktop environments.

LAMMPS GUI thus makes it easier for beginners to get started running simple LAMMPS simulations. It is very suitable for tutorials on LAMMPS since you only need to learn how to use a single program for most tasks and thus time can be saved and people can focus on learning LAMMPS. It is also designed to keep the barrier low when you decide to switch to a full featured, standalone programming editor and more sophisticated visualization and analysis tools and run LAMMPS from a command line.

The following text provides a detailed tour of the features and functionality of the LAMMPS GUI.

Suggestions for new features and reports of bugs are always welcome. You can use the the same channels as for LAMMPS itself for that purpose.

Main window

When LAMMPS GUI starts, it will show a main window with either an empty buffer or the contents of a loaded file. In the latter case it may look like the following:


There is the typical menu bar at the top, then the main editor buffer, and a status bar at the bottom. The input file contents are shown with line numbers on the left and the input is colored according to the LAMMPS input file syntax. The status bar shows the status of LAMMPS execution on the left (e.g. “Ready.” when idle) and the current working directory on the right. The name of the current file in the buffer is shown in the window title; the word *modified* is added if the buffer edits have not yet saved to a file. The size of the main window will be stored when exiting and restored when starting again.

Opening Files

The LAMMPS GUI application will try to open the first command line argument as a LAMMPS input script, further arguments are ignored. When no argument is given, LAMMPS GUI will start with an empty buffer. Files can also be opened via the File menu or by drag-and-drop of a file from a graphical file manager into the editor window. Only one file can be open at a time, so opening a new file with a filled buffer will close the buffer. If the buffer has unsaved modifications, you will be asked to either cancel the operation, discard the changes, or save them.

Running LAMMPS

From within the LAMMPS GUI main window LAMMPS can be started either from the Run menu using the Run LAMMPS from Editor Buffer entry, by the keyboard shortcut Ctrl-Enter (Command-Enter on macOS), or by clicking on the green “Run” button in the status bar. All of these operations will cause LAMMPS to process the entire input script, which may contain multiple run or minimize commands.

LAMMPS runs in a separate thread, so the GUI stays responsive and is able to interact with the running calculation and access data it produces. It is important to note that running LAMMPS this way is using the contents of the input buffer for the run (via the lammps_commands_string() function of the LAMMPS C-library interface), and not the original file it was read from. Thus, if there are unsaved changes in the buffer, they will be used. As an alternative, it is also possible to run LAMMPS by reading the contents of a file from the Run LAMMPS from File menu entry or with Ctrl-Shift-Enter. This option may be required in some rare cases where the input uses some functionality that is not compatible with running LAMMPS from a string buffer. For consistency, any unsaved changes in the buffer must be either saved to the file or undone before LAMMPS can be run from a file.


While LAMMPS is running, the contents of the status bar change. On the left side there is a text indicating that LAMMPS is running, which will also show the number of active threads, if thread-parallel acceleration was selected in the Preferences dialog. On the right side, a progress bar is shown that displays the estimated progress for the current run command.

Also, the line number of the currently executed command will be highlighted in green.


If an error occurs (in the example below the command label was incorrectly capitalized as “Label”), an error message dialog will be shown and the line of the input which triggered the error will be highlighted. The state of LAMMPS in the status bar will be set to “Failed.” instead of “Ready.”


Up to three additional windows will open during a run:

  • a log window with the captured screen output

  • a chart window with a line graph created from the thermodynamic output of the run

  • a slide show window with images created by a dump image command

More information on those windows and how to adjust their behavior and contents is given below.

An active LAMMPS run can be stopped cleanly by using either the Stop LAMMPS entry in the Run menu, the keyboard shortcut Ctrl-/ (Command-/ on macOS), or by clicking on the red button in the status bar. This will cause the running LAMMPS process to complete the current timestep (or iteration for energy minimization) and then complete the processing of the buffer while skipping all run or minimize commands. This is equivalent to the input script command timer timeout 0 and is implemented by calling the lammps_force_timeout() function of the LAMMPS C-library interface. Please see the corresponding documentation pages to understand the implications of this operation.

Log Window

By default, when starting a run, a “Log Window” will open that displays the current screen output of the LAMMPS calculation, that would normally be seen in the command line window, as shown below.


LAMMPS GUI captures the screen output as it is generated and updates the log window regularly during a run.

By default, the log window will be replaced each time a run is started. The runs are counted and the run number for the current run is displayed in the window title. It is possible to change the behavior of LAMMPS GUI in the preferences dialog to create a new log window for every run or to not show the current log window. It is also possible to show or hide the current log window from the View menu.

The text in the log window is read-only and cannot be modified, but keyboard shortcuts to select and copy all or parts of the text can be used to transfer text to another program. Also, the keyboard shortcut Ctrl-S (Command-S on macOS) is available to save the log buffer to a file. The “Select All” and “Copy” functions, as well as a “Save Log to File” option are also available from a context menu by clicking with the right mouse button into the log window text area.

Chart Window

By default, when starting a run, a “Chart Window” will open that displays a plot of thermodynamic output of the LAMMPS calculation as shown below.


The drop down menu on the top right allows selection of different properties that are computed and written to thermo output. Only one property can be shown at a time. The plots will be updated with new data as the run progresses, so they can be used to visually monitor the evolution of available properties. The window title will show the current run number that this chart window corresponds to. Same as explained for the log window above, by default, the chart window will be replaced on each new run, but the behavior can be changed in the preferences dialog.

From the File menu on the top left, it is possible to save an image of the currently displayed plot or export the data in either plain text columns (for use by plotting tools like gnuplot or grace), or as CSV data which can be imported for further processing with Microsoft Excel or pandas

Thermo output data from successive run commands in the input script will be combined into a single data set unless the format, number, or names of output columns are changed with a thermo_style or a thermo_modify command, or the current time step is reset with reset_timestep, or if a clear command is issued.

Image Slide Show

By default, if the LAMMPS input contains a dump image command, a “Slide Show” window will open which loads and displays the images created by LAMMPS as they are written.


The various buttons at the bottom right of the window allow single stepping through the sequence of images or playing an animation (as a continuous loop or once from first to last). It is also possible to zoom in or zoom out of the displayed images, and to export the slide show animation to a movie file, if ffmpeg is installed.

Variable Info

During a run, it may be of interest to monitor the value of input script variables, for example to monitor the progress of loops. This can be done by enabling the “Variables Window” in the View menu or by using the Ctrl-Shift-W keyboard shortcut. This will show info similar to the info variables command in a separate window as shown below.


Like the log and chart windows, its content is continuously updated during a run. It will show “(none)” if there are no variables defined. Note that it is also possible to set index style variables, that would normally be set via command line flags, via the “Set Variables…” dialog from the Run menu. LAMMPS GUI will automatically set the variable “gui_run” to the current value of the run counter. That way it would be possible to automatically record a log for each run attempt by using the command

log logfile-${gui_run}.txt

at the beginning of an input file. That would record logs to files logfile-1.txt, logfile-2.txt, and so on for successive runs.

Viewing Snapshot Images

By selecting the Create Image entry in the Run menu, or by hitting the Ctrl-I (Command-I on macOS) keyboard shortcut, or by clicking on the “palette” button in the status bar, LAMMPS GUI will send a custom write_dump image command to LAMMPS and read the resulting snapshot image with the current state of the system into an image viewer window. This functionality is not available during an ongoing run. When LAMMPS is not yet initialized, LAMMPS GUI will try to identify the line with the first run or minimize command and execute all command up to that line from the input buffer and then add a “run 0” command. This will initialize the system so an image of the initial state of the system can be rendered. If there was an error, the snapshot image viewer will not appear.

When possible, LAMMPS GUI will try to detect which elements the atoms correspond to (via their mass) and then colorize them in the image accordingly. Otherwise the default predefined sequence of colors is assigned to the different atom types.


The default image size, some default image quality settings, the view style and some colors can be changed in the Preferences dialog window. From the image viewer window further adjustments can be made: actual image size, high-quality (SSAO) rendering, anti-aliasing, view style, display of box or axes, zoom factor. The view of the system can be rotated horizontally and vertically. It is also possible to only display the atoms within a group defined in the input script (default is “all”). After each change, the image is rendered again and the display updated. The small palette icon on the top left will be colored while LAMMPS is running to render the new image; it will be grayed out when it is finished. When there are many atoms to render and high quality images with anti-aliasing are requested, re-rendering may take several seconds. From the File menu of the image window, the current image can be saved to a file or copied into the cut-n-paste buffer for pasting into another application.

Editor Functions

The editor has most of the usual functionality that similar programs have: text selection via mouse or with cursor moves while holding the Shift key, Cut (Ctrl-X), Copy (Ctrl-C), Paste (Ctrl-V), Undo (Ctrl-Z), Redo (Ctrl-Shift-Z), Select All (Ctrl-A). When trying to exit the editor with a modified buffer, a dialog will pop up asking whether to cancel the exit operation, or to save or not save the buffer contents to a file.

Context Specific Word Completion

By default, LAMMPS GUI will display a small pop-up frame with possible choices for LAMMPS input script commands or styles after 2 characters of a word have been typed.


The word can then be completed through selecting an entry by scrolling up and down with the cursor keys and selecting with the ‘Enter’ key or by clicking on the entry with the mouse. The automatic completion pop-up can be disabled in the Preferences dialog, but the completion can still be requested manually by either hitting the ‘Shift-TAB’ key or by right-clicking with the mouse and selecting the option from the context menu. Most of the completion information is taken from the LAMMPS instance and thus it will be adjusted to only show available options that have been enabled while compiling LAMMPS. That, however, excludes accelerated styles and commands; for improved clarity, only the non-suffix version of styles are shown.

Line Reformatting

The editor supports reformatting lines according to the syntax in order to have consistently aligned lines. This primarily means adding whitespace padding to commands, type specifiers, IDs and names. This reformatting is performed by default when hitting the ‘Enter’ key to start a new line. This feature can be turned on or off in the Preferences dialog, but it can still be manually performed by hitting the ‘TAB’ key. The amount of padding can also be changed in the Preferences dialog.

Internally this functionality is achieved by splitting the line into “words” and then putting it back together with padding added where the context can be detected; otherwise a single space is used between words.

Context Specific Help


A unique feature of the LAMMPS GUI is the option to look up the documentation for the command in the current line. This can be done by either clicking the right mouse button or by using the Ctrl-? keyboard shortcut. When clicking the mouse there are additional entries in the context menu that will open the corresponding documentation page in the online LAMMPS documentation. When using the keyboard, the first of those entries will be chosen directly.


The Preferences dialog allows customization of the behavior and look of the LAMMPS GUI application. The settings are grouped and each group is displayed within a tab.

guiprefs1 guiprefs2 guiprefs3 guiprefs4

General Settings:

  • Echo input to log: when checked, all input commands, including variable expansions, will be echoed to the log window. This is equivalent to using -echo screen at the command line. There is no log file produced by default, since LAMMPS GUI uses -log none.

  • Include citation details: when checked full citation info will be included to the log window. This is equivalent to using -cite screen on the command line.

  • Show log window by default: when checked, the screen output of a LAMMPS run will be collected in a log window during the run

  • Show chart window by default: when checked, the thermodynamic output of a LAMMPS run will be collected and displayed in a chart window as line graphs.

  • Show slide show window by default: when checked, a slide show window will be shown with images from a dump image command, if present, in the LAMMPS input.

  • Replace log window on new run: when checked, an existing log window will be replaced on a new LAMMPS run, otherwise each run will create a new log window.

  • Replace chart window on new run: when checked, an existing chart window will be replaced on a new LAMMPS run, otherwise each run will create a new chart window.

  • Replace image window on new render: when checked, an existing chart window will be replaced when a new snapshot image is requested, otherwise each command will create a new image window.

  • Path to LAMMPS Shared Library File: this option is only visible when LAMMPS GUI was compiled to load the LAMMPS library at run time instead of being linked to it directly. With the Browse.. button or by changing the text, a different shared library file with a different compilation of LAMMPS with different settings or from a different version can be loaded. After this setting was changed, LAMMPS GUI needs to be re-launched.

  • Select Default Font: Opens a font selection dialog where the type and size for the default font (used for everything but the editor and log) of the application can be set.

  • Select Text Font: Opens a font selection dialog where the type and size for the text editor and log font of the application can be set.

  • GUI update interval: Allows to set the time interval between GUI and data updates during a LAMMPS run in milliseconds. The default is to update the GUI every 100 milliseconds. This is good for most cases. For LAMMPS runs that run very fast, however, data may be missed and through lowering this interval, this can be corrected. However, this will make the GUI use more resources, which may be a problem on some computers with slower CPUs. The default value is 100 milliseconds.


This tab enables selection of an accelerator package for LAMMPS to use and is equivalent to using the -suffix and -package flags on the command line. Only settings supported by the LAMMPS library and local hardware are available. The Number of threads field allows setting the maximum number of threads for the accelerator packages that use threads.

Snapshot Image:

This tab allows setting defaults for the snapshot images displayed in the Image Viewer window, such as its dimensions and the zoom factor applied. The Antialias switch will render images with twice the number of pixels for width and height and then smoothly scale the image back to the requested size. This produces higher quality images with smoother edges at the expense of requiring more CPU time to render the image. The HQ Image mode option turns on screen space ambient occlusion (SSAO) mode when rendering images. This is also more time consuming, but produces a more ‘spatial’ representation of the system shading of atoms by their depth. The VDW Style checkbox selects whether atoms are represented by space filling spheres when checked or by smaller spheres and sticks. Finally there are a couple of drop down lists to select the background and box colors.

Editor Settings:

This tab allows tweaking settings of the editor window. Specifically the amount of padding to be added to LAMMPS commands, types or type ranges, IDs (e.g. for fixes), and names (e.g. for groups). The value set is the minimum width for the text element and it can be chosen in the range between 1 and 32.

The two settings which follow enable or disable the automatic reformatting when hitting the ‘Enter’ key and the automatic display of the completion pop-up window.

Keyboard Shortcuts

Almost all functionality is accessible from the menu of the editor window or through keyboard shortcuts. The following shortcuts are available (On macOS use the Command key instead of Ctrl/Control).








New File


Undo edit


Run Input


Open File


Redo edit


Stop Active Run


Save File


Copy text


Set Variables


Save File As


Cut text


Snapshot Image


Quit Application


Paste text


Slide Show


Close Window


Select All






Quick Help






Context Help


Show Variables


Run File


Reformat line


Show Completions

Further editing keybindings are documented with the Qt documentation. In case of conflicts the list above takes precedence.

All other windows only support a subset of keyboard shortcuts listed above. Typically, the shortcuts Ctrl-/ (Stop Run), Ctrl-W (Close Window), and Ctrl-Q (Quit Application) are supported.