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📄️ Pseudo potentials

A pseudopotential is an approximation used in electronic structure calculations that replaces the strong Coulomb potential of the nucleus and the effect of tightly-bound core electrons with a weaker, effective potential acting only on the valence electrons . This approach is based on the chemical observation that core electrons are essentially "frozen" and do not participate in bonding, allowing the valence electrons to be described by smoother pseudo-wavefunctions . In Quantum ESPRESSO, a plane-wave pseudopotential code , this approximation is fundamental as it makes calculations computationally feasible by drastically reducing the required number of plane waves and eliminating the need to describe rapid wavefunction oscillations near the nucleus . The code supports modern norm-conserving and ultrasoft pseudopotentials, with ultrasoft types being particularly valuable as they allow for even lower plane-wave energy cutoffs, speeding up calculations without sacrificing accuracy.