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【答案】应助回帖
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youzhizhe(金币+3, 1ST强帖+1): 谢谢交流。 2011-08-25 23:38:45
我分析了一下那几步的计算，的确第6步需要第4步的chk
第3步使用第1或第2步的都行
第6步和第7步计算是和第3步的两个计算相对应，只不过第6/7步是发射，第3步是激发，第6/7两步得到的能量之差就是经过指定态的溶剂化效应校正之后的荧光发射能量，经过转换可以得到荧光的发射波长。
关于平衡和非平衡的问题是和statespecific计算有着不可分的关系的，你可以看一下下面的英文部分，这是我前一段时间从Gaussian官方技术顾问那里得到的详细解释，几句话精练不出来，翻译也要耗费一段时间，你耐心读一读。
另外，如果你是用的是Gaussian 09 A.01或者A.02，请使用ExternalIteration或者SelfConsistent代替Statespecific选项，因为后者有点问题，如果是G09 B.01，用这三个选项之一都行，意义相同。
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The "StateSpecific" approach in this context applies to the excited state, and yes it involves solving self-consistently the "fast" component of the solvent polarization for the target state and non-equilibrium solvation for the "slow" component of the solvent polarization (i.e. the "slow" component of the solvent polarization comes from the origin state).
The total polarization is always partitioned into two components, "slow" and "fast". The "slow" part can be regarded as the reorganization of the solvent molecules as a response to a change in the electronic density of the solute. The "fast" part can be regarded as the response of the electrons in the solvent to a change in the electronic density of the solute. For a change in the electronic density of the solute such as a vertical electronic transition, the "slow" component of the polarization is much slower than the timescale of the electronic transition, so the solvent does not have time to respond in this way to the vertical electronic transition. The "fast" component of the polarization, on the other hand, is closer in timescale to the vertical electronic transition on the solute.
In an equilibrium solvation calculation, both components are in equilibrium with the solute's density. By default, all ground state calculations assume equilibrium solvation, as well as geometry optimizations of excited states (and also any calculation that involves the computation of the relaxed density of the excited state). Again, in equilibrium solvation processes, both the "slow" and "fast" component of the solvent polarization are in equilibrium with the excited state density.
In the case of a TD energy calculation (no excited state density or geometry optimization) for the computation of a vertical electronic excitation, the default is to do a non-equilibrium process. For this case then, the "fast" component of the polarization "responds" to the change in the solute density from ground to excited state, but the "slow" component did not have time to "respond" so it still comes from the one that was in equilibrium with the solute's ground state density. This is the case of both "Step 2" and "Step 3" in the example shown in the manual.
In "Step 2", an energy calculation using TD is performed, thus it defaults to non-equilibrium solvation. The solvation effects on the excited states energies are computed by means of a linear response approach. The absorption energies via the linear response approach only are those reported directly in the output of this "Step 2" job.
In "Step 3", a step further is taken and a correction of the linear response excitation energy is performed by solving the "fast" component of the solvent polarization self-consistently with the selected excited state density (the "State-Specific" approach). This is generally an improvement over the excitation energies obtained by linear response alone. Note that since this "State-Specific" approach involves the calculation of the excited state density, the program would default to doing an equilibrium solvation calculation on the excited state. However, the goal of "Step 3" is to compute the vertical excitation energy, so as mentioned above, we would like to use the "slow" component of the solvent polarization from the ground state calculation (in "Step 3", the first part does an equilibrium calculation on the ground state saving the solvent reaction field to the checkpoint file) and solving self-consistently the "fast" component with the excited state density (the second part of "Step 3" reads the reaction field from the checkpoint file, the one from the ground state calculation, keeps the "slow" component as is, and solves the "fast" component self-consistently with the excited state density). The absorption energy via the "State-Specific" approach is the energy difference between the excited state energy after all PCM corrections from the non-equilibrium calculation in "Step 3" and the ground state energy resulting from the equilibrium process (either first part of "Step 3" or final, optimized geometry, energy from "Step 1", the two ground state energies should be the same).
In a TD geometry optimization of an excited state, since one is looking for the equilibrium geometry, the default is to do equilibrium solvation, so the two components, "slow" and "fast", of the polarization are in equilibrium with the solute's excited state density. All "Step 4", "Step 5" and "Step 6" use equilibrium solvation for the selected excited state.
The emission energy (vertical energy of the excited to ground state transition) by means of a linear response approach can be found in the output of "Step 4". For the final (optimized) geometry in "Step 4", the "excitation energy" shown in this output would be equal to the emission energy since it is the result of an equilibrium calculation on the selected excited state.
"Step 6" and "Step 7" are analogous to the two parts of "Step 3" but this time for the opposite transition (excited to ground states). Thus, "Step 6" is analogous to the first part of "Step 3", it is an equilibrium calculation on the origin state (now the excited state) in which both "slow" and "fast" components of solvent polarization are solved self-consistently with the excited state density (this calculation can be regarded as a correction of the excited state energy beyond the linear response approach, which was done in "Step 4" . Now, this "Step 6" saves the solvent reaction field to the checkpoint file. "Step 7" reads this information from the file (just like the second part of "Step 3" and performs a non-equilibrium calculation of the ground state energy, using the "slow" component of the solvent polarization from the excited state calculation ("Step 6" and only doing the "fast" component of the solvent polarization self-consistent with the ground state density. The emission energy via the "State-Specific" approach would be the energy difference between the excited state energy after all PCM corrections from "Step 6" and the ground state energy resulting from the non-equilibrium process in "Step 7". |
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