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小木虫论坛-学术科研互动平台 » 计算模拟区 » 量子化学 » Gaussian » 【求助】如何计算在溶剂中的发射波长？
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tephoon78

木虫 (正式写手)

[交流] 【求助】如何计算在溶剂中的发射波长？已有3人参与

（1）在计算吸收波长时，
Excited State   1: Singlet-A   3.2076 eV 386.53 nm  f=0.0014  =0.000
      12 -> 13        -0.70615
意味着电子从12轨道到13轨道的跃迁。但是在使用td计算发射光谱的时候，计算结果也类似，也会出现
Excited State   1: Singlet-A   2.159eV 326.53 nm  f=0.0026  =0.000
      12 -> 13        -0.8396
那么这个12 -> 13  该如何解释？


（2)      
在Gaussian 09 user’s reference (page 249-252)给出的例子，让人看不明白。例子的解释如下：
第1步优化基态几何结构和频率。
第2步计算线性垂直激发能。
第3步分成2步，首先保留基态的溶剂效应，并写入chk文件；再次，从chk文件中读溶剂效应，然后计算线性垂直激发能。
第4步是激发态的几何优化。
第5步是计算频率。
到这一步，前面的步骤都是可以理解的，下面的两步让人看不明
第6步保留激发的溶剂效应，并写入chk文件。
第7步使用B3LYP方法计算，而不是TD.
既然第4步是激发态几何构型优化，那么它的溶剂效应就是激发态的。在这一步可以直接得到波长。第6、7两步纯粹多余。
即使是第6步保存了溶剂效应，第7步的B3lyp并不能计算得到波长，而是计算能量的。
谁能解释一下？


我将这个例子复制下来。
Fluoresence example: Emission (Fluorescence) from First Excited State (n→π*) of Acetaldehyde
Here we study the cycle:

Acetaldehyde Excitation and Emission Cycle
The primary process of interest is the emission, but this example shows how to study the complete cycle including the solvent effects.
Step 1: Ground state geometry optimization and frequencies (equilibrium solvation). This is a standard Opt Freq calculation on the ground state including PCM equilibrium solvation.
%chk=01-ac
# B3LYP/6-31+G(d,p) Opt Freq SCRF=(Solvent=Ethanol)

Acetaldehyde ground state

0 1
C
C,1,RA
X,2,1.,1,A
O,2,RB,3,A,1,180.,0
X,1,1.,2,90.,3,0.,0
H,1,R1,2,A1,5,0.,0
H,1,R23,2,A23,5,B23,0
H,1,R23,2,A23,5,-B23,0
H,2,R4,1,A4,3,180.,0

RA=1.53643
RB=1.21718
R1=1.08516
R23=1.08688
R4=1.10433
A=62.1511
A1=110.51212
A23=109.88119
A4=114.26114
B23=120.56468
Step 2: Vertical excitation with linear response solvation. This is a TD-DFT calculation of the vertical excitation, therefore at the ground state equilibrium geometry, with the default solvation: linear response, non-equilibrium. We perform a single-point TD-DFT calculation, which defaults to non-equilibrium solvation. The results of this job will be used to identify which state or states are of interest and their ordering. These results give a reasonable description of the solvation of the excited state, but not quite as good as that from a state-specific solvation calculation. In this case, we see that the n->π* state is the first excited state. Next, we will use the state-specific method to produce a better description of the vertical excitation step.
%chk=02-ac
# B3LYP/6-31+G(d,p) TD=NStates=6 SCRF=(Solvent=Ethanol)
  Geom=Check Guess=Read

Acetaldehyde: linear response vertical excited states

0 1
Step 3: State-specific solvation of the vertical excitation. This will require two job steps: first the ground state calculation is done, specifying NonEq=write in the PCM input section, in order to store the information about non-equilibrium solvation based on the ground state. Second, the actual state-specific calculation is done, reading in the necessary information for non-equilibrium solvation using NonEq=read.
%chk=03-ac
# B3LYP/6-31+G(d,p) SCRF=(Solvent=Ethanol,Read)
  Geom=Check Guess=Read

Acetaldehyde: prepare for state-specific non-eq solvation
by saving the solvent reaction field from the ground state

0 1

NonEq=write

--link1--
%chk=03-ac
# B3LYP/6-31+G(d,p) TD(NStates=6,Root=1)
  SCRF=(Solvent=Ethanol,StateSpecific,Read)
  Geom=Check Guess=Read

Acetaldehyde: read non-eq solvation from ground state and
compute energy of the first excited with the state-specific method

0 1

NonEq=read
Step 4: Relaxation of the excited state geometry. Next, we perform a TD-DFT geometry optimization, with equilibrium, linear response solvation, in order to find the minimum energy point on the excited state potential energy surface. Since this is a TD-DFT optimization, the program defaults to equilibrium solvation. As is typical of such cases, the molecule has a plane of symmetry in the ground state but the symmetry is broken in the excited state, so the ground state geometry is perturbed slightly to break symmetry at the start of the optimization.
%chk=04-ac
# B3LYP/6-31+G(d,p) TD=(Read,NStates=6,Root=1) SCRF=(Solvent=Ethanol)
  Geom=Modify Guess=Read Opt=RCFC

Acetaldehyde: excited state opt
Modify geometry to break Cs symmetry
since first excited state is A"

0 1

4 1 2 3 10.0
5 1 2 7 -50.0
Step 5: Vibrational frequencies of the excited state structure. Now we run a frequency calculation to verify that the geometry located in step 4 is a minimum. The results could also be used as part of a Franck-Condon calculation if desired (see below). This is a numerical frequency calculation.
%chk=05-ac
# B3LYP/6-31+G(d,p) TD=(Read,NStates=6,Root=1) Freq
  SCRF=(Solvent=Ethanol) Geom=Check Guess=Read

Acetaldehyde excited state freq

0 1
Step 6: Emission state-specific solvation (part 1). This step does state-specific equilibrium solvation of the excited state at its equilibrium geometry, writing out the solvation data for the next step via the PCM NonEq=write input.
%chk=06-ac
# B3LYP/6-31+G(d,p) TD=(Read,NStates=6,Root=1)
  SCRF=(Solvent=Ethanol,StateSpecific,Read)
  Geom=Check Guess=Read

Acetaldehyde emission state-specific solvation
at first excited state optimized geometry

0 1

NonEq=write
Step 7: Emission to final ground state (part 2). Finally, we compute the ground state energy with non-equibrium solvation, at the excited state geometry and with the static solvation from the excited state.
%chk=07-ac
# B3LYP/6-31+G(d,p) SCRF=(Solvent=Ethanol,Read) Geom=Check Guess=Read

Acetaldehyde: ground state non-equilibrium
at excited state geometry.

0 1

NonEq=read
Steps 1, 2, and 4 would be sufficient to compute the excitation and emission energies in the gas-phase (along with step 5 to confirm the nature of stationary point). They are not sufficient when solvent effects are included because the energies computed in step 4 correspond to the ground state solvent reaction field, while the emission takes place in the reaction field created in response to the excited state charge distribution. This is what is accounted for properly in steps 6 and 7.

[ Last edited by tephoon78 on 2010-6-6 at 08:10 ]
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abbott

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小木虫(金币+0.5):给个红包，谢谢回帖交流
aylayl08(金币+1):谢谢 2010-06-04 14:00:38
请看前页 你就能明白.

另 这个说明书上的算例  有部分错误. 请注意核查
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tephoon78

木虫 (正式写手)
能说的详细点吗？
我的理解对吗？
谢谢！
引用回帖:
Originally posted by abbott at 2010-06-03 17:33:31:
请看前页 你就能明白.

另 这个说明书上的算例  有部分错误. 请注意核查

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3楼2010-06-04 14:01:05
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faqianliu

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4楼2010-06-04 19:32:27
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loovfnd

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我用这套方法做，总出错。
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5楼2011-03-26 15:40:32
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pwzhou

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tephoon78(金币+20): 2011-03-26 16:56:11
引用回帖:
Originally posted by tephoon78 at 2010-06-03 15:46:34:
（1）在计算吸收波长时，
Excited State   1: Singlet-A   3.2076 eV 386.53 nm  f=0.0014  <S**2>=0.000
      12 -> 13        -0.70615
意味着电子从12轨道到13轨道的跃迁。但是在使用td计算发射光 ...

请看这个帖子：http://muchong.com/bbs/viewthread.php?tid=2826231&fpage=1
我已经在回复中给出了Gaussian公司关于这个例子的一些详细的解释。另外，有啥不明白的可以看看Gaussian在这个部分引用的3篇JCP的文献，看看State－Specific和line Response到底有什么区别。
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6楼2011-03-26 15:46:39
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