When I calculate the self-consistent field (SCF) using the hybrid functional (HSE), the calculation stopped without crashing, and the following line appeared at the end: 'Using ACE for calculation of exact exchange'. How can I resolve this problem?
The HSE (Heyd-Scuseria-Ernzerhof) functional is a widely used method in density functional theory (DFT) calculations for the accurate description of electronic structures of materials. However, there can be some issues with the HSE calculation using the Quantum ESPRESSO code, which is a popular software package for DFT calculations. Here are some common problems and possible solutions:
Convergence issues: HSE calculations are computationally expensive, and may require more iterations to achieve convergence compared to simpler DFT calculations. This can lead to convergence issues, especially for large systems. To address this, one can increase the number of k-points or the plane-wave cutoff, or use a better initial guess for the electronic wavefunction.
Memory requirements: HSE calculations can also require a lot of memory, especially for larger systems. To address this, one can use parallel computing with more processors or reduce the size of the system being studied.
Difficulty in choosing the screening parameter: The HSE functional requires the selection of a screening parameter (omega) to balance the exchange-correlation energy with the screened Coulomb potential. Choosing the optimal omega value can be challenging, and may require some trial and error or parameter tuning.
Dependence on pseudopotentials: The HSE functional is sensitive to the choice of pseudopotentials used in the calculation, which can affect the accuracy of the results. One should ensure that the pseudopotentials used are appropriate for the elements being studied and the type of calculation being performed.
Overall, while there can be some challenges with HSE calculations using the Quantum ESPRESSO code, many of these can be addressed with appropriate parameter settings, computational resources, and careful selection of input parameters