This directory contains all the necessary data, codes, and notebooks to reproduce the results of the paper titled "A new non-linear instability for scalar fields" (https://arxiv.org/abs/2107.14215). This paper has also been published as a letter in Physical Review D and can be found in Volume 105, Issue 2, article id.L021304, which can be accessed at this link: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.105.L021304. Directories Codes: This directory contains different codes used to generate and post-process the simulation data, including k-evolution and Latfield2. Simulations_data: This directory includes the data for the scalar field snapshots, information about the average of the scalar field, and power spectra. Figure_notebooks: This directory includes Jupyter notebooks to reproduce the figures presented in the paper. How to Use Download the files to your local machine. Navigate to the directory where the files are saved. Install the necessary packages Navigate to the "Figure_notebooks" directory and open the Jupyter notebooks in your preferred environment. Run the cells in the notebooks to reproduce the figures. Navigate to the "codes" directory and use the appropriate code to generate and post-process the simulation data. Navigate to the "data" directory to access the simulation data. If you have any feedback or request feel free to email farbod.hassani@gmail.com