CCL:G: Natural Transition Orbitals

 Sent to CCL by: Tobias Kraemer [Tobias.Kraemer\a/mu.ie]
 Dear Tian,
 Thanks for your detailed answer, this has helped to clarify things a lot.
 Tobias
 Dr. Tobias Krämer
 Lecturer in Inorganic Chemistry
 Department of Chemistry
 Maynooth University, Maynooth, Co. Kildare, Ireland.
 E: tobias.kraemer+*+mu.ie   T: +353 (0)1 474 7517
 -----Original Message-----
 > From: owner-chemistry+tobias.kraemer==mu.ie+*+ccl.net [mailto:owner-chemistry+tobias.kraemer==mu.ie+*+ccl.net] On Behalf Of Tian
 Lu sobereva**sina.com
 Sent: 26 February 2018 23:32
 To: Tobias Kraemer <Tobias.Kraemer+*+mu.ie>
 Subject: CCL:G: Natural Transition Orbitals
 Sent to CCL by: "Tian  Lu" [sobereva],[sina.com] Dear Tobias Kraemer,
 Please do not forget to check eigenvalues of NTO pairs, they reflects
 contribution of each NTO pair to the electronic excitation. Although NTO
 analysis works well for most cases, namely only one dominating NTO pair could be
 found; however, NTO analysis is not always useful, because there are also many
 cases the NTO pair with largest eigenvalue doesn't contribute to nearly 100% (or
 >85%) of electronic excitation, and thus you still have to simultaneously
 inspecting more than one pair of orbitals to fully understand the character of
 the excitation.
 If you suspect if the NTO analysis result you obtained is completely correct,
 you can also use Multiwfn program to carry out NTO analysis and compare the
 result (for Gaussian user, .fch file and Gaussian output file are needed as
 input file, see Section 4.18.4 of the Multiwfn manual for example, you will find
 the use is rather easy). The additional advantage of using Multiwfn to perform
 NTO analysis is that the resulting NTOs can be directly visualized and analyzed
 (i.e. calculating orbital composition, evaluating position of orbital centroid,
 etc.) in the code, and when you want to respectively analyze NTO for many
 states, you do not need to repeat Gaussian calculation multiple times (Gaussian
 is only needed to run once, and then using the resulting files, in Multiwfn you
 can directly select the state to generate NTO).
 By the way, when NTO analysis is not as useful as expected due to aforementioned
 reason, you can consider to use the hole-electron analysis in Multiwfn instead,
 see Section 3.21.1 of the manual for introduction and Section 4.18.1 for
 example. In any case, this analysis represents the excitation as transition from
 "hole" to "electron", therefore by simply visualizing hole
 distribution and electron distribution (they can be drawn as isosurfaces in the
 same map in Multiwfn), you will be able to fully capture the character of the
 electronic excitation.
 Best wishes,
 Tian Lu
 ----- Original Message -----
 Sent to CCL by: "Tobias Kraemer" [tobias.kraemer---mu.ie] Hello
 everybody, I have performed TD-DFT calculations on an organic molecule using
 G09(D.01), and analysed the excitations by means of the Natural Transition
 Orbital scheme.
 In most cases the situation is pretty clear cut, and the NTOs provide a
 straigthforward way to "visualise" the transitions. However, I am
 confused by a result for one state, in which the CI coefficients for two
 contributing transitions are -0.45 (HOMO-2 -> LUMO) and 0.51 (HOMO ->
 LUMO+2). To me this suggests that these MO pairs have almost equal
 LUMO+weight
 in the expansion, which should be reflected in the NTOs. However, the particle
 NTO very much resembles the canonical HOMO. Would this be expected? I would have
 thought that the NTO should look different in this case, but perhaps I am wrong
 here. I wouldn't assume that these are simply a sum of the two, since they are
 obtained by a SVD procedure.
 To generate these I pretty much follow a standard protocol, reading the .chk
 file from the TD job into a new calculation with this route section #
 Geom=AllCheck ChkBas Guess=(Read,Only) Density=(Check,Transition=n)
 Pop=(NTO,SaveNTO)
 Then I use formcheck and cubegen to generate the plot for the respective
 transition "n" (so, individual jobs for each transition are run).
 In this context I also wondered how to obtain the associated weight
 (sigma) of a NTO pair. I have seen these in some publications, presented along
 with the excitation energy and oscillator strength.
 Thanks for you helphttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp-:-//www.ccl.net/chemistry/sub_unsub.shtmlhttp-:-//www.ccl.net/spammers.txt