Issue in cell-relax calculation about abacus-develop

[WHUweiqingzhou]

@pxlxingliang could you have a look?

[dyzheng]

Can you upload your INPUT files in this Issue?

[kogareru1z]

test.zip

[kogareru1z]

Can you upload your INPUT files in this Issue?

I have upload my file, please check it

[pxlxingliang]

I did some tests, and found abacus may raise the error of " trust radius is too small! Break down" after the first change of cell (some times raising error after 3 or 4 changes of cell).

I have noticed that the energy after cell-changed may be not consistent with the energy of single SCF job. (I use the STRU after several cell-changed to run a single SCF job, and energy in these two calculations are different.) This is not a unique issue for ABACUS, and similar issues can also occur in other software using planewave basis.

Initially, I suspect it is the inconsistent of energy leads to the error. So, I try to do the same calculation with LCAO basis, but abacus also raise the same error in the 13-th ION step of 2nd cell relax. This indicate there may have some bugs in the BFGS algorithm.

[pxlxingliang]

Here is the energies of each ION step in the LCAO cell-relax

     1	 final etot is -7626.8581853 eV
     2	 final etot is -7626.59287266190 eV
     3	 final etot is -7627.31601440061 eV
     4	 final etot is -7627.30152822028 eV
     5	 final etot is -7627.32129424860 eV
     6	 final etot is -7627.32430508587 eV
     7	 final etot is -7627.32440163847 eV
     8	 final etot is -7627.32463978079 eV
     9	 final etot is -7627.32466417965 eV
    10	 final etot is -7627.32473436150 eV
Here begining the relax after the changed cell
    11	 final etot is -7627.34799569358 eV
    12	 final etot is -7627.34588754335 eV
    13	 final etot is -7627.34583180096 eV
    14	 final etot is -7627.34580092413 eV
    15	 final etot is -7627.34578563616 eV
    16	 final etot is -7627.34577840438 eV
    17	 final etot is -7627.34577504755 eV
    18	 final etot is -7627.34577350336 eV
    19	 final etot is -7627.34577279541 eV
    20	 final etot is -7627.34577247129 eV
    21	 final etot is -7627.34577232235 eV
    22	 final etot is -7627.34577225479 eV
    23	 final etot is -7627.34577225895 eV

The energy in the first cell loop decrease normally, but after 11 step, the energy is increasing.

[kogareru1z]

The energy in the first cell loop decrease normally, but after 11 step, the energy is increasing.

How can I solve this issue? Is it necessary to use another relaxation method?

[pxlxingliang]

The energy in the first cell loop decrease normally, but after 11 step, the energy is increasing.

How can I solve this issue? Is it necessary to use another relaxation method?

Suggest you to do cell-relax by using cg, and I will figure out this issue ASAP.

[pxlxingliang]

As QE also has BFGS trust region method to do the cell relax, I try to use QE doing the vc-relax, and it is converged in 47 relax stps.