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["Quan Phung Manh" <manhquank9@gmail.com>]

Dear Abinit users

 I am wondering about the accuracy of Abinit. When I optimized a system, I fond that:

 (This is a part of a Broyden step)

BROYDEN STEP NUMBER   0  ------------------------------------------------------

.....

 Cartesian coordinates (bohr)

  0.00000000000000E+00 -4.02974775563795E-06  5.73138604166224E+00

  0.00000000000000E+00  6.13867555717564E+00  1.25214153616492E+01

  0.00000000000000E+00 -1.86741688703378E-06  1.81132671801313E+01

.....

 Cartesian forces (hart/bohr); max,rms= 2.55847E-02 6.79451E-03 (free atoms)

 -0.00000000000000E+00 -1.28251108101439E-06 -9.45167776806339E-05

 -0.00000000000000E+00  3.25755754385893E-06 -5.80951371185085E-03

 -0.00000000000000E+00 -2.54621291199277E-07 -4.14769847396469E-03

 

 BROYDEN STEP NUMBER   1  ------------------------------------------------------

.....

 Cartesian coordinates (bohr)

  0.00000000000000E+00 -5.31225883665235E-06  5.73129152488456E+00

  0.00000000000000E+00  6.13867881473318E+00  1.25156058479374E+01

  0.00000000000000E+00 -2.12203817823307E-06  1.81091194816573E+01

.....

 Cartesian forces (hart/bohr); max,rms= 2.98782E-02 8.35903E-03 (free atoms)

 -0.00000000000000E+00 -2.48375052932897E-08 -5.29091999454351E-04

 -0.00000000000000E+00 -1.05349352878470E-06 -3.70632293405876E-03

 -0.00000000000000E+00 -1.14816794074730E-06 -4.24804883657326E-03

 

 BROYDEN STEP NUMBER   2  ------------------------------------------------------

.....

 Cartesian coordinates (bohr)

  0.00000000000000E+00 -6.13335378372791E-06  5.73756793492669E+00

  0.00000000000000E+00  6.13869431998394E+00  1.25550789073397E+01

  0.00000000000000E+00  1.14550021043293E-05  1.81565540341853E+01

 

I found a connection between Broyden step number 1 and 2. The difference between Cartesian coordinates is base on Cartesian forces

For example:

5.73129152488456E+00-5.73138604166224E+00=-9.45167776806339E-05  (same sign and value with the force)

1.25156058479374E+01-1.25214153616492E+01=-5.80951371185085E-03  (same sign and value with the force)

                                                 

But between Broyden step number 2 and 3.

5.73756793492669E+00-5.73129152488456E+00=0.00627641         (different sign and value -5.29091999454351E-04)

1.25550789073397E+01-1.25156058479374E+01=0.039473059       (different sign and value -3.70632293405876E-03)

 

Most of Broyden steps, I found this connection (at least same sign)

But sometimes, I found the "different sign" I when this happened, the total energy increase after SCF.

I don't understand why? Please tell me how can I reject this error?

 

Best regarded

Quan Phung Manh

--
Quan Phung Manh
Khoa Hoá học - ĐH Khoa học tự nhiên - 19 Lê Thánh Tông Hà Nội
ĐT: 0906263816