update documents

Author: mohanchen

docs/advanced/elec_properties/Mulliken.md

@@ -1,7 +1,7 @@
 # Mulliken Charge Analysis
 
 From version 2.1.0, ABACUS has the function of Mulliken population analysis. The example can be found in [examples/mulliken](https://github.com/deepmodeling/abacus-develop/tree/develop/examples/mulliken). \
-To use this function, set [out_mul](./input-main.md#out_mul) to `1` in the INPUT file. After calculation, there will be an output file named `mulliken.txt` in the output directory. In MD calculations, the output interval is controlled by the keyword [out_interval](./input-main.md#out_interval). In the file, there are contents like (`nspin 1`):
+To use this function, set [out_mul](./input-main.md#out_mul) to `1` in the INPUT file. After calculation, there will be an output file named `mulliken.txt` in the output directory. In MD calculations, the output interval is controlled by the keyword [out_freq_ion](./input-main.md#out_freq_ion). In the file, there are contents like (`nspin 1`):
 
 ```
 STEP: 0

docs/advanced/elec_properties/hs_matrix.md

@@ -45,7 +45,7 @@ The CSR format stores a sparse m × n matrix M in row form using three (one-dime
   - The arrays V and COL_INDEX are of length NNZ, and contain the non-zero values and the column indices of those values respectively.
   - The array ROW_INDEX is of length m + 1 and encodes the index in V and COL_INDEX where the given row starts. This is equivalent to ROW_INDEX[j] encoding the total number of nonzeros above row j. The last element is NNZ , i.e., the fictitious index in V immediately after the last valid index NNZ - 1.
 
-For calculations involving ionic movements, the output frequency of the matrix is controlled by [out_interval](../input_files/input-main.md#out_interval) and [out_app_flag](../input_files/input-main.md#out_app_flag). 
+For calculations involving ionic movements, the output frequency of the matrix is controlled by [out_freq_ion](../input_files/input-main.md#out_freq_ion) and [out_app_flag](../input_files/input-main.md#out_app_flag). 
 
 ## get_s
 We also offer the option of only calculating the overlap matrix without running SCF. For that purpose, in `INPUT` file we need to set the value keyword [calculation](../input_files/input-main.md#calculation) to be `get_s`.

docs/advanced/elec_properties/position_matrix.md

@@ -18,7 +18,7 @@ Each file or each section of the appended file starts with "STEP: " followed by
 
 Each block here contains the matrix for the corresponding cell. There are three columns in each block, giving the matrix elements in x, y, z directions, respectively. There are altogether nbasis * nbasis lines in each block, which emulates the matrix elements.
 
-In molecular dynamics (MD) calculations, if [out_app_flag](../input_files/input-main.md#out_app_flag) is set to true, then `data-rR-tr` is written in an append manner. Otherwise, output files will be put in a separate directory, `matrix`, and named as `$x`_data-rR-tr, where `$x` is the number of MD step. In addition, the output frequency is controlled by [out_interval](../input_files/input-main.md#out_interval). For example, if we are running a 10-step MD with out_interval = 3, then `$x` will be 0, 3, 6, and 9.
+In molecular dynamics (MD) calculations, if [out_app_flag](../input_files/input-main.md#out_app_flag) is set to true, then `data-rR-tr` is written in an append manner. Otherwise, output files will be put in a separate directory, `matrix`, and named as `$x`_data-rR-tr, where `$x` is the number of MD step. In addition, the output frequency is controlled by [out_freq_ion](../input_files/input-main.md#out_freq_ion). For example, if we are running a 10-step MD with out_freq_ion = 3, then `$x` will be 0, 3, 6, and 9.
 
 ## get_s
 We also offer the option of only calculating the position matrix without running SCF. For that purpose, in `INPUT` file we need to set the keyword [calculation](../input_files/input-main.md#calculation) to `get_s`, and [out_mat_r](../input_files/input-main.md#out_mat_r) to `true`.