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tephoon78木虫 (正式写手)
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【求助】如何计算在溶剂中的发射波长？ 已有3人参与
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（1）在计算吸收波长时， Excited State 1: Singlet-A 3.2076 eV 386.53 nm f=0.0014 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 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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2楼2010-06-03 17:33:31
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tephoon78(金币+20): 2011-03-26 16:56:11
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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。 |
6楼2011-03-26 15:46:39
