The interactive interface replaces manual calculation keyword specification. The type of calculation (e.g. geometrical optimization, frequency calculation, etc.) and level of theory are simply chosen for the desired software package configured. Fields for additional parameters appear in the interface when required. For example, constrained optimizations require the end-user to enter the constraints based on the atomic numbering of the input structure. Consequently, this structure is displayed in the 3D molecular viewer integrated in the interface, and numbering appears when a calculation that requires atom numbering is selected. Finally, custom keywords can also be appended to the input file to not limit the possibilities to what is explicit in the interface and allow more advanced users to customize the input for a given QM software suite fully. Settings can then be saved as preset and later reused. It is important to note that the interface does not change depending on the software package used, making it effortless for the users to use multiple ones. Cal-cUS currently interfaces with Gaussian, 22 ORCA 23-25 and the xTB suite. These packages are of course not provided with CalcUS due to the licensing requirements and must be installed on either local machine that will perform the calculations, or the remote HPC resources used.