# 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`: 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.

For `basis_type=lcao`, only `init_wfc=file` triggers reading existing wavefunctions. LCAO wavefunctions initialize the density matrix and real-space charge density. ABACUS reads text `wf*_nao.txt` files generated with [`out_wfc_lcao=1`](../elec_properties/wfc.md) from `read_file_dir`; binary files generated with `out_wfc_lcao=2` are not supported. The files must use a compatible NAO basis, match the current k-point and spin setup, and contain enough bands. Normal `init_wfc=file` reading matches files written with the default `out_app_flag=true`, which have no geometry-step index. Files written under `WFC/` with a `g*` geometry-step index when `out_app_flag=false` are not matched automatically.

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

For `calculation=get_wf` or `calculation=get_pchg`, `init_wfc` is automatically set to `file`. If `basis_type=lcao_in_pw` is also used, the final value is `nao`.