Docs: Update documentation of dft_functional

Author: ahxbcn

docs/advanced/input_files/input-main.md

@@ -1073,7 +1073,20 @@ calculations.
 
 - **Type**: String
 - **Description**: In our package, the XC functional can either be set explicitly using the `dft_functional` keyword in `INPUT` file. If `dft_functional` is not specified, ABACUS will use the xc functional indicated in the pseudopotential file.
-  On the other hand, if dft_functional is specified, it will overwrite the functional from pseudopotentials and performs calculation with whichever functional the user prefers. We further offer two ways of supplying exchange-correlation functional. The first is using 'short-hand' names such as 'LDA', 'PBE', 'SCAN'. A complete list of 'short-hand' expressions can be found in [the source code](../../../source/source_hamilt/module_xc/xc_functional.cpp). The other way is only available when ***compiling with LIBXC***, and it allows for supplying exchange-correlation functionals as combinations of LIBXC keywords for functional components, joined by a plus sign, for example, dft_functional='LDA_X_1D_EXPONENTIAL+LDA_C_1D_CSC'. The list of LIBXC keywords can be found on its [website](https://libxc.gitlab.io/functionals/). In this way, **we support all the LDA,GGA and mGGA functionals provided by LIBXC**.
+  On the other hand, if dft_functional is specified, it will overwrite the functional from pseudopotentials and performs calculation with whichever functional the user prefers. We further offer two ways of supplying exchange-correlation functional. The first is using 'short-hand' names. A complete list of 'short-hand' expressions can be found in [the source code](../../../source/source_hamilt/module_xc/xc_functional.cpp). Supported density functionals are:
+  - LDA functionals
+    - LDA (equivalent with PZ and SLAPZNOGXNOGC), PWLDA
+  - GGA functionals
+    - PBE (equivalent with SLAPWPBXPBC), PBESOL, REVPBE, WC, BLYP, BP(referred to BP86), PW91, HCTH, OLYP, BLYP_LR
+  - meta-GGA functionals
+    - SCAN (require LIBXC)
+  - Hybrid functionals
+    - PBE0, HF
+    - If LIBXC is avaliale, additional short-hand names of hybrid functionals are supported: HSE(referred to HSE06), B3LYP, LC_PBE, LC_WPBE, LRC_WPBE, LRC_WPBEH, CAM_PBEH, WP22, CWP22, MULLER (equivalent with POWER)
+  - Hybrid meta-GGA functionals
+    - SCAN0 (require LIBXC)
+
+   The other way is only available when ***compiling with LIBXC***, and it allows for supplying exchange-correlation functionals as combinations of LIBXC keywords for functional components, joined by a plus sign, for example, dft_functional='LDA_X_1D_EXPONENTIAL+LDA_C_1D_CSC'. The list of LIBXC keywords can be found on its [website](https://libxc.gitlab.io/functionals/). In this way, **we support all the LDA,GGA and mGGA functionals provided by LIBXC**. Some popular functionals and their usage are: RPBE of [Hammer et al.](https://journals.aps.org/prb/abstract/10.1103/PhysRevB.59.7413), set `dft_functional` to 'GGA_X_RPBE+GGA_C_PBE', and [r$^{2}$SCAN](https://pubs.acs.org/doi/10.1021/acs.jpclett.0c02405), set `dft_functional` to 'MGGA_X_R2SCAN+MGGA_C_R2SCAN'.
 
   Furthermore, the old INPUT parameter exx_hybrid_type for hybrid functionals has been absorbed into dft_functional. Options are `hf` (pure Hartree-Fock), `pbe0`(PBE0), `hse` (Note: in order to use HSE functional, LIBXC is required). Note also that HSE has been tested while PBE0 has NOT been fully tested yet, and the maximum CPU cores for running exx in parallel is $N(N+1)/2$, with N being the number of atoms.