[molpro-user] Mixed derivatives in Numerical Hessian

[Werner Győrffy]

Dear Aleksandr,

Numerical Hessians in Molpro are computed by using central finite 
differences with a 2-point formula as a default. That is a "general 
formula". That gives accurate results in most of the cases. There is a 
trade-off between accuracy and efficiency: More accurate finite field 
calculations would increase the number of single point calculations 
significantly. If one needs more accurate Hessians, it can be done only 
by computing that manually by using procedures.

Regards,

Werner.

On 02/04/2017 02:04 AM, Aleksandr Lykhin wrote:
> Does anybody know how Molpro calculates mixed derivatives using central
> differences? It seems like it generates only two mixed displacements
> instead of four, so the general formula cannot be applied directly.
>
> --
> Kind regards, Aleksandr O. Lykhin.
>
>
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