From owner-chemistry@ccl.net Mon Aug 11 07:57:01 2014 From: "Liang XU 13480022 ~ life.hkbu.edu.hk" To: CCL Subject: CCL:G: 3 Questions about Gaussian 09: TDDFT/TDA, negative/imaginary excitation, de-excitation Message-Id: <-50394-140811010215-31182-OkerM5aPo9KU/0+1mSdr7A:server.ccl.net> X-Original-From: Liang XU <13480022%a%life.hkbu.edu.hk> Content-Type: multipart/alternative; boundary=089e0116091ef42d400500537465 Date: Mon, 11 Aug 2014 13:02:07 +0800 MIME-Version: 1.0 Sent to CCL by: Liang XU [13480022(!)life.hkbu.edu.hk] --089e0116091ef42d400500537465 Content-Type: text/plain; charset=UTF-8 Dear CCL subscribers, I have Three questions about running TDDFT, TDHF, and CIS with Gaussian 09, Revision C.01, that need your help. Thank you so much in advance for your suggestions, advices, and comments. ------------------------------------------------ (1) TDA for removing Negative/Imaginary excitation energy : In TDDFT, TDHF, CIS calculations, using Gaussian, some excitation energies are written as negative values, e.g., ******************** TD B3LYP; excitation energy = -0.6141 eV : Excited State 1: Triplet-SGU -0.6141 eV -2019.02 nm f=-0.0000 =2.000 4 -> 5 0.80601 4 -> 10 -0.11570 4 <- 5 0.39989 ******************** Note: the above problem of negative excitation energy, which could be originated from the instability of wave function, still persists even I used "Stable=Opt" in Gaussian. Some papers actually refer these negative values as "imaginary" numbers or imaginary excitation energies (e.g., see DOI: 10.1063/1.2786997 and 10.1021/cr0505627 ). And the papers also show that the imaginary excitation energies could be re-calculated to become "real" excitation energies by Tamm-Dancoff Approximation (TDA). ->> Since there is No TDA available in the Revision C.01 of Gaussian 09, I just wonder a bit is it correct that the TDA implemented in the Revision D.01 of Gaussian 09 can be used to perform TDA-DFT (e.g., TDA-B3LYP) calculations that may possibly solve the above problem of Negative/Imaginary excitation energy ? ------------------------------------------------ ------------------------------------------------ (2) Normalization procedure for "de-excitation" : In a TDDFT calculation, we found, e.g., ******************** TD B3LYP: Excited State 1: 3.003-?Sym 0.1776 eV 6981.48 nm f=0.0000 =2.004 5A -> 6A 1.03714 5A <- 6A 0.28145 ******************** The above coefficient of "5A -> 6A" is already larger than unity (1.03714 > 1.0). And we have another coefficient for the de-excitation "5A <- 6A", 0.28145 . Interestingly, (1.03714)^2 - (0.28145)^2 = 0.996. ->> So, I just wonder a bit is it true that if there is a coefficient associated with de-excitation, then the square of this coefficient should be subtracted (instead of being added) during a normalization process ? ------------------------------------------------ ------------------------------------------------ (3) Physical meaning for "de-excitation" : Just a quick follow-up question about de-excitation. ->> I just wonder a bit whether or not there is any physical meaning for de-excitation, e.g., the above "5A <- 6A" ? ->> Or, is it just a pure mathematical construct as what this paper, DOI: 10.1021/jp308662x , suggested ? ------------------------------------------------ Just feel free to give me any suggestions, advices, and comments. Thank you very much in advance again. Regards, Liang Xu -- Ph.D student Department of Physics Hong Kong Baptist University Primary E-mail : 13480022 _ life.hkbu.edu.hk Secondary E-mail : xuliangaioros _ gmail.com --089e0116091ef42d400500537465 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Dear CCL subscribers,


=C2=A0 I have Three questions about running TDDFT, TDHF, and CIS with= Gaussian 09, Revision C.01, that need your help.
=C2=A0 Thank you so much in advance for your suggestions, advices, and comm= ents.

--------------------------= ----------------------
(1)=C2=A0 TDA= for removing Negative/Imaginary excitation energy :

=C2=A0 In TDDFT, TDHF, CIS calculat= ions, using Gaussian, some excitation energies are written as negative valu= es, e.g.,
********************
TD= B3LYP; excitation energy =3D=C2=A0 -0.6141 eV :

=C2=A0Excited State=C2=A0=C2= =A0 1:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Triplet-SGU=C2=A0=C2=A0=C2=A0 -0.6141 = eV=C2=A0=C2=A0=C2=A0 -2019.02 nm=C2=A0 f=3D-0.0000=C2=A0 <S**2>=3D2.0= 00
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 4 ->=C2=A0 5=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 0.80601
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 4 -> 10=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 -0.11570
=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 4 <-=C2=A0 5=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0 0.39989
********************
Note: the above problem of negative excitatio= n energy, which could be originated from the instability of wave function, = still persists even I used "Stable=3DOpt" in Gaussian.

Som= e papers actually refer these negative values as "imaginary" numb= ers or imaginary excitation energies (e.g., see DOI:=C2=A010.1063/1.2786997=C2= =A0and=C2=A010.1021/cr0505627=C2=A0).
And the papers also show that the imaginary excitation energies could be re= -calculated to become "real" excitation energies by Tamm-Dancoff = Approximation (TDA).

->> S= ince there is No TDA available in the Revision C.01 of Gaussian 09, I just = wonder a bit is it correct that the TDA implemented in the Revision D.01 of= Gaussian 09 can be used to perform TDA-DFT (e.g., TDA-B3LYP) calculations = that may possibly solve the above problem of Negative/Imaginary excitation = energy ?
------------------------------------------------
-----------------------= -------------------------
(2)=C2=A0 = Normalization procedure for "de-excitation" :

In a TDDFT calculation, we found, e.g.,
********************
TD B3LYP:

=C2=A0Excited State=C2=A0=C2=A0 1:=C2=A0 3.003-?Sym=C2=A0=C2= =A0=C2=A0 0.1776 eV 6981.48 nm=C2=A0 f=3D0.0000=C2=A0 <S**2>=3D2.004<= br> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 5A ->=C2=A0 6A=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 1.03714
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 5A <-=C2=A0 6A= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 0.28145
***************= *****

The above coefficient of "5A ->=C2=A0 6A" is alre= ady larger than unity (1.03714 > 1.0).=C2=A0 And we have another coeffic= ient for the de-excitation "5A <-=C2=A0 6A", 0.28145 .

Interestingly, (1.03714)^2 - (0.28145)^2 =3D 0.996.

->> So= , I just wonder a bit is it true that if there is a coefficient associated = with de-excitation, then the square of this coefficient should be subtracte= d (instead of being added) during a normalization process ?=C2=A0
------------------------------------------------
-----------------------= -------------------------
(3)=C2=A0 = Physical meaning for "de-excitation" :

Just a quick follow-up question abo= ut de-excitation.

->> I ju= st wonder a bit whether or not there is any physical meaning for de-excitat= ion, e.g., the above "5A <-=C2=A0 6A" ?
->> Or, is it just a pure mathematical construct as what this paper, = DOI:=C2=A010.1021/jp308662x=C2=A0, suggested ?
------------------------------------------------

=C2=A0 Just feel free to give me an= y suggestions, advices, and comments.
=C2=A0 Thank you very much in advance= again.

Regards,
Liang Xu

--

Ph= .D student
Department of Physics
Hong Kong Baptist University
Prim= ary E-mail :=C2=A013480022 _ life.hkbu.edu.hk
Secondary E-mail :=C2=A0xuliangaioros _ gmail.com
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