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--- howto:gw [2021/04/21 20:19] – jwilhelm
+++ howto:gw [2021/04/21 20:43] – [4. Self-consistent GW calculations] jwilhelm
@@ Line 150: / Line 150: @@
 An exemplary input for a parallel calculation can be found in the supporting information of [[doi>10.1021/acs.jctc.6b00380]] [2]. The emphasis is on the parameters SIZE_FREQ_INTEG_GROUP and NUMBER_PROC which should be increased for larger calculations. In case of a too small number, the code will crash due to out of memory while a too large number results in slow speed. Typically, one starts for large-scale calculations from a small molecule. When increasing the system size, the parameters SIZE_FREQ_INTEG_GROUP and NUMBER_PROC should be both increased to avoid a crash due to out of memory. The maximum number for both parameters is the number of MPI tasks. Also, the number of nodes should be increased with $N^3_\text{atoms}$ to account for the scaling of the memory of GW.
-===== 4. Self-consistent GW calculations =====
+===== 4. Self-consistent GW calculations and DFT starting point =====
-The G0W0@PBE HOMO value is not in good agreement with the experimental ionization potential of water (12.62 eV). A possible explanation is that PBE may not be a good starting point for G0W0 calculations for molecules in the gas phase, see e.g. [[doi>10.1021/ct300835h]].
+The G0W0@PBE HOMO value of the H2O molecule (~ -12.0 eV) is not in good agreement with the experimental ionization potential (12.62 eV). Benchmarks on molecules and solids indicate that self-consistency of eigenvalues in the Green's function G improves the agreement between the GW calculation and experiment. This scheme is called GW0@PBE and is our favorite GW flavor so far (experience based on nano-sized aromatic molecules). You can also check [[https://www.youtube.com/watch?v=1vUuethWhbs&t=5563s|this video]] or [[>>doi]] on which GW scheme could be good for your system
 ===== 5. Periodic GW calculations =====
 For periodic GW calculations, a special correction scheme is necessary. A similar problem is appearing in Hartree-Fock calculations. In HF, an easy way out is given by the truncation of the Coulomb operator which works due to the convenient form of the HF equations. GW does not exhibit this convenient form and therefore, this truncation does not work for GW calculations. The theory why a correction is necessary and the correction scheme is described in [[doi>10.1103/PhysRevB.95.235123]] [7].