Siesta

mix: Pulay -- inversion failed, > SVD

Asked by David Guzman

Hello Nick,

I got this message while running a geometry minimization during the SCF cycle:
mix: Pulay -- inversion failed, > SVD

There is no information about this in the manual but I believe this has to do with the algorithm used to solve the DIIS equations.
Can you please comment on this issue? Should I be concerned about possible errors in the electronic structure?

Thank you so much,
David

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Nick Papior (nickpapior) said : 		#1

No you should not be worried.

It is a notification that the diis could not find an inverse to the coefficient matrix. Said matrix will typically become singular when very close to convergence or when two iterations in the history become very similar (there are other cases). However the diis problem can also be solved using svd, and in siesta (since 4.1) when a singular matrix is encountered it backfalls to the svd routine and only use the important coefficients. Prior versions would fallback to a linear mixing (although I can't recall if an error message in shown)

If you want you can also always use the svd method. But generally they behave very similar.

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David Guzman (guzmand) said : 		#2

Perfect! Thanks for your answer