Issue using mixed calculation

Francesco Ambrosio francesco... at
Thu Jan 8 12:20:10 UTC 2015

Dear cp2k users and developers.

I want to use thermodynamic integration (TI) to compute differences in 
energies of a Cl vacancy defect in NaCl with two different states of charge 
(0 and +1). If my procedure is correct the result obtained by TI 
(integration of vertical energy gaps) should equal the result obtained by 
energy difference of the energy minima of NaCl(+1) and NaCl(0) relaxed 
structures. The latter are easily computed. In order to compute the 
vertical energy gaps at intermediate steps, I use a mixed calculation 
(input attached). Basically, I aim to optimize the intermediate structures 
(at different values of the coupling parameter) and hence compute the 
vertical gap from wavefunction optimizations with n and n-1 electrons. 
Nevertheless, the results I am obtaining are quite worrying because I 
obtain different intermediate optimized geometries if I use as starting 
structure the relaxed NaCl(+1) or the NaCl(0) respectively and the final 
structures are close to the initial ones. I thought of a possible mistake 
of my input but if I set lambda=0 and lambda=1 I recover the correct 
optimized structures of NaCl(+1) and NaCl(0), no matter the starting point. 
Do you have any thoughts about this based on your experience?

Thank you for your courtesy and your kindness

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