Dear Quantum ESPRESSO Community, I am currently engaged in variable-cell Car-Parrinello (vc-cp) simulations and encountering a persistent issue regarding the evolution of electronic kinetic energy. Despite a systematic variation of time-step values (dt) between 1 to 5 atomic units (a.u.) and fictitious electronic masses (emass) from 50 to 500 a.u., there is a consistent increase in electronic kinetic energy. This trend persists even with a conservative choice of dt=1 a.u. and emass=50 a.u. (Please see the attached image) The subject of my study is an insulating material, confirmed through pw.x calculations using the PBE-GGA, which reveals a band gap of approximately 2 eV. Given this band gap, one would expect the system to adhere to stable Car-Parrinello dynamics within the adiabatic regime. I am reaching out to inquire if there are alternative parameters or aspects of the simulation protocol that could be adjusted to ensure the maintenance of adiabaticity in the system. Furthermore, I am interested in any insights regarding the potential influence of the initial conditions or pseudopotentials that may be contributing to this nonphysical increase in kinetic energy. I would greatly appreciate any guidance or suggestions from the community that could aid in resolving this issue. Thank you for your time and assistance.
Kind regards, Vinay Maithani IIT, Kharagpur
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