CamCASP/Bugs/9
CamCASP => Bugs => Errors in Second-order Energies
Background
Way back in 2010, while developing a potential for molecule XVI (part of the 2010 Blind test), we had encountered large errors in the second-order energies for dimers of this molecule. Sally had alerted us to this (she was developing the potential with my help). She had realised there was a problem as there were significant outliers in the total energies and dispersion energies when compared with our fits. Closer investigation revealed that the contributions to the dispersion energy at imaginary frequency were erratic, and in some cases, even changed sign (they should all be of one sign and decay as <math> 1/(w^2+w_0^2)</math>), where <math>w_0</math> is a characteristic frequency). At that point we brushed aside the problem as there wasn't time to investigate it. But we knew that it was related to the new propagator module that allows us to calculate the FDDS entirely within CamCASP using the ALDAX+CHF model.
Recently, I have encountered the problem yet again, this time with the pyridine dimer. As before, the calculations involve the new propagator module with the ALDAX+CHF model. Unfortunately, this seems to be a large-system problem. Calculations on smaller systems or large systems with smaller (less-diffuse) basis sets have not exhibited the problem. Nor has there been a problem with calculations using the ALDAX propagator.
Here I present a summary of my investigations with a few pyridine dimer systems.
Details
Unless stated, the calculations use the parameters defined here.
CamCASP:
trunk rev 22218
DALTON
Version 2 with patches from Rafal. Also includes changes suggested by Anthony to get it to compile with ifort. See CamCASP/Compilation for details.
Default run parameters:
Integral switch = 1 PBE0 ALDAX+CHF Standard integration grids
Machines used:
Tati:
ifort Version 11.1
BLAS/LAPACK: Goto2
mmp12:
ifort Version 12.0.5
BLAS/LAPACK: ATLAS 3.8.4 with LAPACK additions from Netlib
Compiled with Gfortran 4.5 or 4.6 (probably 4.5)
Gfortran: Versions 4.5.4 and 4.6.1
Example 1: Pyridine
