# Initializing SCF
Good initializing would abate the number of iteration steps in SCF.
Charge density should be initialed for constructing the initial hamiltonian operator.

In PW basis, wavefunction should be initialized for iterate diagonalization method.
In LCAO basis, wavefunction can be read to calculate initial charge density. The wavefunction itself does not have to be initialized.

## Charge Density
`init_chg` is used for choosing the method of charge density initialization.
 - `atomic` : initial charge density by atomic charge density from pseudopotential file under keyword `PP_RHOATOM`
 - `file` : initial charge density from files produced by previous calculations with [`out_chg 1`](../elec_properties/charge.md).
 - `auto`: Abacus first attempts to read the density from a file; if not found, it defaults to using atomic density.
 - `dm` (LCAO only): initial charge density from density matrix files in CSR format. For `nspin=1`, reads `dmrs1_nao.csr`. For `nspin=2` (spin-polarized), reads both `dmrs1_nao.csr` (spin-up) and `dmrs2_nao.csr` (spin-down). These files are generated by previous calculations with [`out_dmr 1`](../elec_properties/density_matrix.md). This method is particularly useful for restarting spin-polarized calculations.
 - `hr` (LCAO only): initial charge density from Hamiltonian matrix files in CSR format. The Hamiltonian is read from file, then diagonalized to obtain wavefunctions and charge density. For `nspin=1`, reads `hrs1_nao.csr`. For `nspin=2` (spin-polarized), reads both `hrs1_nao.csr` (spin-up) and `hrs2_nao.csr` (spin-down). These files are generated by previous calculations with [`out_hsr 1`](../input_files/input-main.md#out_hsr).

## Wavefunction

`init_wfc` selects how wavefunction coefficients are initialized. The available options and behavior depend on `basis_type`.

For `basis_type=pw`, the available options are:

* `atomic`: Use atomic pseudo wavefunctions from `PP_PSWFC`. If no `PP_PSWFC` states are available, all bands are initialized randomly. If the number of atomic states is smaller than `nbands`, the remaining bands are initialized randomly.
* `atomic+random`: If there are at least `nbands` atomic states, apply an approximately 5% multiplicative random perturbation to the atomic initialization. If there are fewer atomic states than `nbands`, use the atomic states and initialize the remaining bands randomly, as for `atomic`.
* `random`: Initialize all bands with random coefficients.
* `nao`: Use numerical atomic orbitals. If the number of NAO states is smaller than `nbands`, the remaining bands are initialized randomly.
* `nao+random`: Apply an approximately 5% multiplicative random perturbation to the NAO initialization; any bands not covered by NAO states are first initialized randomly.
* `file binary`: Read binary `wf*_pw.dat` files generated with [`out_wfc_pw=2`](../elec_properties/wfc.md) from `read_file_dir`. The files must match the current k points, `nbands`, plane-wave layout, and lattice. The `txt` format is not supported for PW wavefunctions.

For `basis_type=lcao`, use `init_wfc file txt` to read text `wf*_nao.txt` files generated with [`out_wfc_lcao=1`](../elec_properties/wfc.md), or `init_wfc file binary` to read binary `wf*_nao.dat` files generated with `out_wfc_lcao=2`, from `read_file_dir`. LCAO wavefunctions initialize the density matrix and real-space charge density. The selected format is required; ABACUS does not automatically detect or fall back to the other format. The files must use a compatible NAO basis, match the current k-point and spin setup, and contain enough bands. Only independent files without geometry-step indices are supported, not files accumulated with `out_app_flag`.

For `basis_type=lcao_in_pw`, `init_wfc` is automatically set to `nao`.

For `calculation=get_wf` or `calculation=get_pchg`, a non-file initialization choice is automatically changed to the file option appropriate for the selected basis. An explicitly selected file format is preserved. If `basis_type=lcao_in_pw` is also used, the final value is `nao`.