LDIAG: Difference between revisions
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Description: This tag determines whether a subspace diagonalization is performed or not within the main algorithm selected by {{TAG|IALGO}}. | Description: This tag determines whether a subspace diagonalization is performed or not within the main algorithm selected by {{TAG|IALGO}}. | ||
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For ALGO=Normal, Fast, and | For ALGO=Normal, Fast, and VeryFast, VASP performs a diagonalization in the subspace spanned by all orbitals. This is often referred to as Rayleigh–Ritz method. The step | ||
increases the convergence rate and thus is expedient in most cases. For the algorithms that optimize | increases the convergence rate and thus is expedient in most cases. For the algorithms that optimize (https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Ritz_method). | ||
For the direct optimization algorithms (for instance ALGO = All or Damped), the subspace diagonalization is usually not performed, but in order to improve | |||
the accuracy of the calculated forces, after convergence has been reached, one single diagonalization in the subspace spanned by all orbitals is performed. | |||
Note that the subspace diagonalization sorts the orbital/eigenvalues in ascending order. | |||
For ALGO = VeryFast, Damped and All, it is possible to switch off the subspace diagonalization by specifying LDIAG=.FALSE. in the INCAR file. | |||
Specifically, for ALGO = VeryFast, LDIAG= .FALSE. changes from an exact Rayleigh–Ritz diagonalization to Loewdin perturbation theory. | |||
Loewdin perturbation theory strictly conserves the orbital order, i.e. the orbitals will be ordered according | |||
to their eigenenergy. For ALGO = Damped and All, the final sub space diagonalization is simply skipped. | |||
Generally using LDIAG = .FALSE. is only advised, if one wants to keep a certain orbital order, for instance when reading the orbitals from an existing WAVECAR file. | |||
== Related Tags and Sections == | == Related Tags and Sections == | ||
{{TAG|IALGO}}, | {{TAG|IALGO}}, | ||
Revision as of 07:02, 10 November 2021
LDIAG = [logical]
Default: LDIAG = .TRUE.
Description: This tag determines whether a subspace diagonalization is performed or not within the main algorithm selected by IALGO.
For ALGO=Normal, Fast, and VeryFast, VASP performs a diagonalization in the subspace spanned by all orbitals. This is often referred to as Rayleigh–Ritz method. The step increases the convergence rate and thus is expedient in most cases. For the algorithms that optimize (https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Ritz_method). For the direct optimization algorithms (for instance ALGO = All or Damped), the subspace diagonalization is usually not performed, but in order to improve the accuracy of the calculated forces, after convergence has been reached, one single diagonalization in the subspace spanned by all orbitals is performed. Note that the subspace diagonalization sorts the orbital/eigenvalues in ascending order.
For ALGO = VeryFast, Damped and All, it is possible to switch off the subspace diagonalization by specifying LDIAG=.FALSE. in the INCAR file. Specifically, for ALGO = VeryFast, LDIAG= .FALSE. changes from an exact Rayleigh–Ritz diagonalization to Loewdin perturbation theory. Loewdin perturbation theory strictly conserves the orbital order, i.e. the orbitals will be ordered according to their eigenenergy. For ALGO = Damped and All, the final sub space diagonalization is simply skipped. Generally using LDIAG = .FALSE. is only advised, if one wants to keep a certain orbital order, for instance when reading the orbitals from an existing WAVECAR file.