Natural orbital transition (NTO)

[eliezer]

Dear all,

it is possible to calculate Natural Orbital Transition (NTO) in TD-DFT with Dalton? Is there any topic about it in the manual?

Best regards,
Eliezer

[taylor]

First, it is difficult to understand how the acronym for "Natural Orbital Transition"can be "NTO" since the words don't match up...

Second, it does not seem that "Natural Orbital Transition" is documented anywhere in the (I would like to claim, as somebody initially responsible...) extensive Dalton manual.

So, I would think the answer, I'm afraid, is "No".

If you feel the Dalton documentation is inadequate, we would very much like to hear how it should be fixed. On the other hand, if there is functionality in the program we document it, so if there isn't documentation, well: you pretty much have to assume that functionality is not there. If it ain't documented in the manual, I gotta tell you, given the effort we've put into this for more than 25 years, that functionality ain't there... If it was, it'd be in the manual. Trust me...

Best regards
Pete

[taylor]

Let me add, because there have been various postings (I admit some of them mine...) on this general topic before. Dalton is focussed on observables. This may not always mean what a doctrinaire quantum chemist might mean by "observable", in the sense of (say) an operator that commutes with the Hamiltonian, but it certainly means something that can be directly connected to experiment, such as polarizability anisotropy <-> bifringence; or electron spin-spin coupling <-> zero-field splitting; let alone things like frequency-dependent hyperpolarizabilities and various sorts of light-scattering experiments. We tend to focus on these sorts of experiments and, as we think of them, observables.

There are many things that chemists want to know, like "populations", and "mechanisms", and "site reactivity", that have been defined enthusiastically by chemists but which have no reality whatsoever in the quantum chemistry world. Mulliken populations, for example (and I am proud to say, because I'm that old, Robert was a mate of mine, really, and I've got the bar/restaurant bills to prove it...) are crap. I will not re-post here because I am so tired of reiterating why this is so this on this forum.

Dalton is focussed on properties that can be measured in the real world. Populations, bond analyses, and (I dare say it) your "Natural Orbital Transition" are part of the world of qualitative, many of us would say "squishy," ideas that have no founding in the mathematical reality of quantum chemistry. It may be that someone will implement these things in Dalton. But I am afraid that most Dalton authors would focus on substance, and will not spend time on"squish". It is not what Dalton is about...

Sorry if this seems harsh: I really don't want to be harsh. Nevertheless: it's observables that count. The squish is meaningless, and therefore irrelevant, and therefore something that just does not get that much attention...

Best regards
Pete

[eliezer]

Dear Pete,

in fact the correct name is Natural Transition Orbitals; so that is why the acronym NTO sounded strange - sorry!
The NTO was proposed only as a "mathematical" procedure to analyse the electronic transitions in TD-DFT calculations (J. Chem. Phys. 2003, 118, 4775). I understand your arguments above and I would like to thank you by the explanations.

Best regards.
Eliezer

[pablo]

Dear Eliezer,

I have implemented NTOs at the TD-HF and TD-DFT level in LSDalton because I needed it.
It is likely that it will be part of the next release but I cannot promise anything.

Best regards,
Pablo