Document socket running log behavior

Author: jianrui geng

docs/advanced/interface/ase.md

@@ -168,6 +168,8 @@ Calling `atoms.get_potential_energy()` is supported, but the ABACUS client still
 
 A socket calculator owns one ABACUS process initialized from one fixed `INPUT`/`STRU` setup. Reuse the same `AbacusSocketIO` instance only for position updates under the same electronic-structure settings and the same cell. Do not change `kpts`, `kspacing`, `nspin`, `basis_type`, `basissets`, pseudopotentials, species, atom count, cell, or other core `INPUT`/`STRU` parameters through an existing socket calculator; create a new `AbacusSocketIO` instance and a new ABACUS client process for those changes. `AbacusSocketIO` rejects cell changes before sending them to ABACUS, and the ABACUS socket driver also checks incoming POSDATA cells against the initial `STRU` cell and exits if they differ.
 
+In socket mode, ABACUS keeps one client process alive. All SCF evaluations produced by the same `AbacusSocketIO` instance are appended to the same `OUT.ABACUS/running_scf.log`, because the ABACUS calculation type remains `scf`. The authoritative per-step energy and force results are returned through the i-PI socket to ASE. Use ASE trajectory and optimizer log files, such as `BFGS(atoms, trajectory="opt.traj", logfile="opt.log")`, when each optimizer or MD step should be saved separately. Treat `running_scf.log` mainly as the ABACUS diagnostic log for the socket client, not as one independent FileIO result per structure.
+
 The i-PI protocol does not transmit element symbols. `AbacusSocketIO` therefore sorts the internal socket atoms with the same first-occurrence species grouping used when writing `STRU`, and maps returned forces back to the original ASE `Atoms` order. This avoids silent force/atom mismatches when structures are read from CIF, extxyz, POSCAR, or other formats whose atom order is not already grouped for ABACUS. Users should not manually reorder atoms for socket I/O; pass the physical ASE `Atoms` object directly to the calculator.
 
 A complete fixed-cell validation and benchmark example is available in `interfaces/ASE_interface/examples/socketio.py`.