考虑溶剂效应的紫外吸收光谱计算.docx

1、采用 PCM 模型计算溶液中的紫外吸收光谱The PCM method in Gaussian 09 includes an external iteration procedure whereby the program computes the energy in solution by making the solvent reaction field self-consistent with the solute electrostatic potential (the latter being generated from the computed electron density

2、with the specified model chemistry).Step 1: Ground state geometry optimization and frequencies (equilibrium solvation 平衡溶剂化：在电子结构不发生改变时，若分子几何结构发生变化则溶剂也跟着变化). This is a standard Opt Freqcalculation on the ground state including PCM equilibrium solvation.获得溶剂中基态稳定几何结构，默认为 Eq 状态%chk=01-ac# B3LYP/6-31+G

3、(d,p) Opt Freq SCRF=(Solvent=Ethanol) Acetaldehyde ground state0 1分子说明(请自行补充)Here is the energy of the ground state optimized geometry in solution:SCF Done: E(RB3LYP) = -153.851761719 A.U. after 1 cyclesStep 2: Vertical excitation with linear response solvation. 默认为 Non-Eq 过程This is a TD-DFT calcula

4、tion 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 o

5、r 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* state(产生第一激发态的跃迁方式) is the first excited state. Next, we will us

6、e the state-specific method to produce a better description of the vertical excitation step.复制以上 step1 中的 01-ac.chk,并将复制文件命名为 02-ac.chk，然后执行如下操作计算紫外跃迁吸收光谱。下边这个计算默认为 non-equilibrium solvation。垂直激发默认为 NonEq过程，但此时没有使用 EI%chk=02-ac# B3LYP/6-31+G(d,p) TD=NStates=6 SCRF=(Solvent=Ethanol) Geom=Check Guess=

7、ReadAcetaldehyde: linear response vertical excited states0 1The vertical excitation (absorption) to first excited state from the non-equilibrium solvation linear response calculation: 发生电子跃迁时，溶剂来不及运动，所以叫做 non-equilibrium solvation linear responseExcited State 1: Singlet-A“ 4.3767 eV 283.28 nm f=0.00

8、00 =0.000 Thus, the ground state to first excited state absorption is at 283.28 nm, computed via the linear-response approach.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 in

9、put section, in order to store the information about non-equilibrium solvation based on the ground state(之前基态优化的时候是 equilibrium solvation linear response 情况下完成的，这里重新改用 NonEq 方法，并将信息保存下来). 查得最后的能量数据为 E(RB3LYP) = -153.851761719Second, the actual state-specific calculation is done, reading in the neces

10、sary information for non-equilibrium solvation using NonEq=read, and specifying the checkpoint file from Step2: 这一步从 step3 的第一步中读取 NonEq 信息，并执行激发态计算，获得垂直激发的能量。查得最后的能量数据为 E(RB3LYP) = -153.850869764。同时会给出 After PCM corrections, the energy is -153.687679830 a.u.由于设定了 Root=1，所以只会给出第一激发态的如下详细信息：This stat

11、e for optimization and/or second-order correction. Copying the excited state density for this state as the 1-particle RhoCI density. 但不知道这个信息有什么用处。最后给出的能量也许是第一激发态弛豫前的能量，而非基态能量.3.1 与 step1 相同，区别在于采用 NonEq=Write 保留了环境状态作为下一步NonEq 过程的状态3.2 针对 3.1 的 NonEq=Write 环境，用 NonEq=Read 读取此环境。采用 SCRF=EI方法使得溶质的第一激

12、发态(Root=1 指定为针对第一激发态)调整 electron density状态，达到与读取环境自洽的状态。注意，3.1 起始几何结构与 3.2 终止几何结构全同，没有改变。3.2 的能量减去 3.1 的能量即为带有溶剂效应矫正后的紫外吸收光谱。复制 01-ac.chk 文件，并将复制后文件重新命名为 03-ac.chk。执行如下计算%chk=03-ac# B3LYP/6-31+G(d,p) SCRF=(Solvent=Ethanol,Read) Geom=Check Guess=Read Acetaldehyde: prepare for state-specific non-eq so

13、lvation by saving the solvent reaction field from the ground state0 1NonEq=write-link1-%chk=03-ac#P B3LYP/6-31+G(d,p) SCRF=(Solvent=Ethanol,ExternalIteration,Read) Geom=Check Guess=Read TD(NStates=6,Root=1)Acetaldehyde: read non-eq solvation from ground state and compute energy of the first excited

14、with the state-specific method0 1NonEq=readHere is the energy of first excited stateat the ground state optimized geometryfrom the non-equilibrium solvation state-specific calculation:After PCM corrections, the energy is -153.687679826 a.u. Subtracting this energy from the ground state energy (from

15、step 1) gives the ground state to first excited state absorption including the state-specific solvation correction: at 277.69 nm. 计算溶剂中的激发吸收光谱！ExternalIteration 方法(EI 方法)的大致含义是：不同于之前常用的标准方法(标准方法中计算溶剂效应时先采用 SCF 方法获得初步结果，然后把溶剂效果当做微扰项叠加到体系中获得体系性质)，EI 方法直接针对溶剂体系的 MP2 结果获得溶剂效果，让溶质自洽于环境溶剂。问题，若在 3.2 中，去除 SCRF=EI 关键词，则能量数值有多大变化，激发波长有多大变化？若能量数值和激发波长均不变，则表示对光谱结果数据没有影响，这样就不叫 state-specific solvation correction 了。所以我想应该是变化了。若变化了，一次只能使用 ROOT=N计算第 N 个激发的具体波长，每次激发单独计算，这样很费事。但我们可以计算振动系数比较大的几个紫外光谱就行了！并不是每个都要计算