[QE-users] Ensuring Adiabaticity in Variable-Cell Car-Parrinello Molecular Dynamics Simulations

[Vinay Maithani]

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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