[molpro-user] RS2 gradient error: WRONG E0 FROM CIGAM0I

Werner Győrffy gyorffy at theochem.uni-stuttgart.de
Mon Sep 25 09:00:49 CEST 2017

Dear Seth,

Could you please post or send me the input of your failing calculation?



On 24.09.2017 02:09, Seth Olsen wrote:
> Hi Molpro Users,
> I have run into the error same previously brought up by Artur Nenov (see 
> email copied below), which arises in the RS2 routine when gradients are 
> calculated.  I have been unable to find further mention of it in the 
> mailing list, and wanted to know if there had been follow-up or if a 
> work-around had been found.  Can the threshold for matching E0 be tuned 
> without recompilation?
> Many Thanks,
> Seth
> ******Original Message from Artur Nenov dated Oct 18 2011******
> Dear Molpro developers,
> I have encountered an error while trying an RS2 optimization in Molpro. It
> occurs while Molpro tries to calculate the gradient in a SS-PT2 or MS-MR-PT2
> step.
> The error output reads
> WRONG E0 FROM CIGAM0I: -34.84434593   -34.84434594 (exemplary numbers)
> and comes after the RESULTS FOR STATE list. The values given after the error
> message give the Zeroth-order valence energy, which is calculated once in the
> begining of the RS2 routine (without level shift) and then recalculated when a
> gradient calculation is requested (this time adding the level shift). The
> error occurs also when no error shift given.
> The error can be straced back to the files cigam2ppi.f (SS-PT2) and
> cigam2ppi_ms.f (MS-MR-PT2), where an accuracy of 1.d-9 for the delta of both
> values is needed, otherwise the program aborts. Obviously, in the given case
> the delta is higher. I all situation where I had this error so far both values
> differ by one or two digits in the very last printed decimal place. Further so
> far this error has not occured with smaller molecules like ethylene or
> cyclohexadiene, only with bigger molecules.
> My question is whether these small discrepances between the Zeroth-order
> valence energies before and after the PT2 correction are due to some numerical
> inconsistence or there is more to it.
> Can I ignore this error (comment the abortion execution signal in the two files
> above) or reduce the accuracy? Is this error somehow connected to the accuracy
> of the calculated gradient?
> Best regards,
> Artur Nenov
> ===========================
> Seth Olsen, PhD.
> Honorary Fellow
> School of Mathematics & Physics
> The University of Queensland
> QLD 4072  Australia
> Ph: +61 7 3365 2816
> ===========================
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