`out_wfc_lcao 2` appends output wavefunction data to initial LCAO wavefunction file read by `init_wfc nao`

[ahxbcn]

Details

Improved SCF Convergence with Proper Initial Charge and Wavefunction Handling

Reading a good initial charge density and wavefunction significantly aids in achieving SCF convergence. However, I encountered an issue when using init_wfc nao to read the LCAO wavefunction file (WFC_NAO_K*.dat) from a previously converged calculation and out_wfc_lcao 2 to write the converged LCAO wavefunction back into the same WFC_NAO_K*.dat file. The output data is written in append mode ("a"), resulting in the WFC_NAO_K*.dat file being concatenated with the new wavefunction data. This behavior prevents the effective use of init_wfc nao and out_wfc_lcao 2 to accelerate SCF convergence when working with ase-abacus and ATST-tools.

Reproducible Example

A minimal example demonstrating this issue is provided here. It includes two calculations for a Si crystal with the same structure:

1. The first calculation, 1-out_wfc_lcao_2, generates the LCAO wavefunction file WFC_NAO_K1.dat and the charge density file Si-CHARGE-DENSITY.restart.
2. These files are then copied to 2_read_chg_wfc/OUT.Si, and the calculation in 2_read_chg_wfc is executed. After completion, the size of WFC_NAO_K1.dat in 2_read_chg_wfc is 30744 bytes, exactly twice the size of the file in 1-out_wfc_lcao_2.

Proposed Fix

After reviewing the source code of ABACUS v3.9.0, I believe this issue stems from the use of Binstream ofs(name, "a"); in module_io/write_wfc_nao.cpp (lines 60 and 136). Would it be appropriate to modify this to Binstream ofs(name, "w"); to overwrite the initial LCAO wavefunction file (WFC_NAO_K*.dat) instead of appending to it?

Have you read FAQ on the online manual http://abacus.deepmodeling.com/en/latest/community/faq.html

• Yes, I have read the FAQ part on online manual.

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