Feature: Support calculation of multi-k point band-decomposed charge density under LCAO basis

docs/advanced/input_files/input-main.md

@@ -158,6 +158,7 @@
     - [rpa](#rpa)
     - [nbands\_istate](#nbands_istate)
     - [bands\_to\_print](#bands_to_print)
+    - [if\_separate\_k](#if_separate_k)
   - [Density of states](#density-of-states)
     - [dos\_edelta\_ev](#dos_edelta_ev)
     - [dos\_sigma](#dos_sigma)
@@ -449,8 +450,8 @@ These variables are used to control general system parameters.
   - **relax**: perform structure relaxation calculations, the `relax_nmax` parameter depicts the maximal number of ionic iterations
   - **cell-relax**: perform cell relaxation calculations
   - **md**: perform molecular dynamics simulations
-  - **get_pchg**: obtain partial charge density (for LCAO basis only). See `nbands_istate` and `bands_to_print` for more information
-  - **get_wf**: obtain wave functions (for LCAO basis only). See `nbands_istate` for more information
+  - **get_pchg**: obtain partial (band-decomposed) charge densities (for LCAO basis only). See `nbands_istate` and `bands_to_print` for more information
+  - **get_wf**: obtain wave functions (for LCAO basis only). See `nbands_istate` and `bands_to_print` for more information
   - **get_S** : obtain the overlap matrix formed by localized orbitals (for LCAO basis with multiple k points). the file name is `SR.csr` with file format being the same as that generated by [out_mat_hs2](#out_mat_hs2)
   - **gen_bessel** : generates projectors, i.e., a series of Bessel functions, for the DeePKS method (for LCAO basis only); see also keywords `bessel_descriptor_lmax`, `bessel_descriptor_rcut` and `bessel_descriptor_tolerence`. A file named `jle.orb` will be generated which contains the projectors. An example is provided in examples/H2O-deepks-pw
   - **test_memory** : obtain a rough estimation of memory consuption for the calculation
@@ -1755,10 +1756,17 @@ The band (KS orbital) energy for each (k-point, spin, band) will be printed in t
 ### bands_to_print
 
 - **Type**: String
-- **Availability**: For both PW and LCAO. When `basis_type = lcao`, only used when `calculation = get_pchg`.
-- **Description**: Specifies the bands to calculate the charge density for, using a space-separated string of 0s and 1s, providing a more flexible selection compared to `nbands_istate`. Each digit in the string corresponds to a band, starting from the first band. A `1` indicates that the charge density should be calculated for that band, while a `0` means the band will be ignored. The parameter allows a compact and flexible notation (similar to [`ocp_set`](#ocp_set)), for example the syntax `1 4*0 5*1 0` is used to denote the selection of bands: `1` means calculate for the first band, `4*0` skips the next four bands, `5*1` means calculate for the following five bands, and the final `0` skips the next band. It's essential that the total count of bands does not exceed the total number of bands (`nbands`); otherwise, it results in an error, and the process exits. The input string must contain only numbers and the asterisk (`*`) for repetition, ensuring correct format and intention of band selection.
+- **Availability**: For both PW and LCAO. When `basis_type = lcao`, used when `calculation = get_wf` or `calculation = get_pchg`.
+- **Description**: Specifies the bands to calculate the wave functions/charge densities for, using a space-separated string of 0s and 1s, providing a more flexible selection compared to `nbands_istate`. Each digit in the string corresponds to a band, starting from the first band. A `1` indicates that the charge density should be calculated for that band, while a `0` means the band will be ignored. The parameter allows a compact and flexible notation (similar to [`ocp_set`](#ocp_set)), for example the syntax `1 4*0 5*1 0` is used to denote the selection of bands: `1` means calculate for the first band, `4*0` skips the next four bands, `5*1` means calculate for the following five bands, and the final `0` skips the next band. It's essential that the total count of bands does not exceed the total number of bands (`nbands`); otherwise, it results in an error, and the process exits. The input string must contain only numbers and the asterisk (`*`) for repetition, ensuring correct format and intention of band selection.
 - **Default**: none
 
+### if_separate_k
+
+- **Type**: Boolean
+- **Availability**: Only for LCAO, used only when `calculation = get_pchg` and `gamma_only` is turned off.
+- **Description**: Specifies whether to write the partial charge densities for all k-points to individual files or merge them. **Warning**: Enabling symmetry may produce incorrect results due to incorrect k-point weights. Therefore, when calculating partial charge densities, it is strongly recommended to set `symmetry = -1`.
+- **Default**: false
+
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 ## Density of states

source/module_base/global_function.h

@@ -161,6 +161,13 @@ static inline void DCOPY(const T& a, T& b, const int& dim)
     }
 }
 
+template <typename T>
+inline void DCOPY(const T* a, T* b, const int& dim) {
+    for (int i = 0; i < dim; ++i) {
+        b[i] = a[i];
+    }
+}
+
 template <typename T>
 inline void COPYARRAY(const T* a, T* b, const long dim);