CCL:G: G09-Excessive mixing of frozen core and valence orbitals

 Sent to CCL by: Susi Lehtola [susi.lehtola%a%alumni.helsinki.fi]
 On 4/6/19 1:19 PM, Jacob Berenbeim jacob.berenbeim*|*york.ac.uk wrote:
 
 Sent to CCL by: "Jacob  Berenbeim" [jacob.berenbeim###york.ac.uk]
 I'm getting inconsistent results with TD-DFT calculations performed
on organic alkali M+(Na+, K+, Rb+) clusters. These systems have previously been optimized and confirmed to be minima at the wb97xd/defsvp level using Gaussian 09. A small number of my low energy cluster structures are terminating early when running TD-DFT from these optimized chk files at the same computational level. I've included the termination dialog below. I'm not using a pseudo potential for most of the terminating cases. I'd appreciate any advice or tips. 
 Dear Jacob,
 this is a well-known issue in calculations with alkali metals: the
 definition of core orbitals by the orbital eigenvalue can lead to the
 wrong orbitals being included in the active space. This problem has been
 described e.g. by Petrie in J. Phys. Chem. A 102, 6138 (1998) and by
 Rassolov, Pople, Redfern and Curtiss in Chemical Physics Letters 350,
 573 (2001).
 The problem is that the semi-core orbitals of the alkali metals can have
 orbital energies that are higher than the valence orbitals of other
 species, which means that the valence orbitals end up frozen while the
 semi-core orbitals are included in the active space of the TD-DFT
 calculation.
 This can be solved either by redefining the core orbitals by studying
 the orbital character visually or via Mulliken analysis like Rassolov et
 al, or by increasing the size of the active space such that all valence
 orbitals are included therein.
 Pierre Archirel already suggested using td=full, which means dropping
 the active space altogether. A less costly option would be to use just a
 slightly larger active space e.g. the inner noble gas core.
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 Mr. Susi Lehtola, PhD             Junior Fellow, Adjunct Professor
 susi.lehtola**alumni.helsinki.fi   University of Helsinki
 http://susilehtola.github.io/     Finland
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 Susi Lehtola, dosentti, FT        tutkijatohtori
 susi.lehtola**alumni.helsinki.fi   Helsingin yliopisto
 http://susilehtola.github.io/
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