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本帖最后由 霜晨月 于 2023-3-30 14:47 编辑
我在计算一个有机小分子与单重态氧气的反应，通过查找以往的帖子，主要根据@wzkchem5 等老师的建议，采用ORCA的Spin-Flip TDDFT，氧气分子的输入文件如下：
! B3LYP def2-TZVP(-f) def2/J RIJCOSX tightSCF opt freq def2-TZVP/C noautostart miniprint nopop
%maxcore 1000
%pal nprocs 2 end
! CPCM(water)
%tddft
SF TRUE
nroots 10
iroot 2 # iroot = 1,2,3,4都分别计算了
end
* xyz 0 3
O 0.42473920 2.19821159 0.00000000
O -0.73686080 2.19821159 0.00000000
*
有几个问题想请教各位老师：
1. 氧气（iroot = 2）的计算结果
SF-TDA EXCITED STATES
---------------------
the weight of the individual excitations are printed if larger than 1.0e-02
(SPIN-FLIP GROUND STATE)
STATE 1: E= 0.068246 au 1.857 eV 14978.2 cm**-1 <S**2> = 2.014936
7a -> 7b : 0.497619 (c= -0.70542124)
8a -> 8b : 0.497620 (c= 0.70542180)
STATE 2: E= 0.077608 au 2.112 eV 17032.9 cm**-1 <S**2> = 0.011657
7a -> 8b : 0.493135 (c= -0.70223575)
8a -> 7b : 0.493135 (c= 0.70223592)
STATE 3: E= 0.077647 au 2.113 eV 17041.5 cm**-1 <S**2> = 0.011657
7a -> 7b : 0.493138 (c= -0.70223782)
8a -> 8b : 0.493137 (c= -0.70223738)
STATE 4: E= 0.087194 au 2.373 eV 19137.0 cm**-1 <S**2> = 0.011583
7a -> 8b : 0.498192 (c= -0.70582740)
8a -> 7b : 0.498192 (c= -0.70582722)
STATE 5: E= 0.323159 au 8.794 eV 70925.3 cm**-1 <S**2> = 1.007191
4a -> 7b : 0.084588 (c= 0.29084045)
4a -> 8b : 0.412432 (c= 0.64220832)
5a -> 7b : 0.412432 (c= -0.64220838)
5a -> 8b : 0.084588 (c= 0.29084046)
显然state 1是三重态（即基态氧气分子），state 2和3都是单重态，但二者能量非常接近，能否简单认为state 2就是第一激发态（实际参与反应的单重态氧气）？但state 1和2的能量差只有24.6 kJ/mol，查到基态氧气与第一激发态的能量差是94 kJ/mol左右，相差太远了。即便是state 4和1的能量差也只有49.7 kJ/mol。
问题2. ORCA手册说这里的state 1就是SF的基态，但这个state 1的能量（STATE 1: E= 0.068246 au 1.857 eV）是相对于谁的呢？应该是相对于SCF能量，但SCF能量又是哪个态的能量呢？
Now, it is very important to consider that the SF ground state is not the UHF ground state
anymore, the "new" ground state within the SF scheme is actually STATE 1. You can think of the UHF
as being only an initial model, on the basis of which the SF states are built. The final energy of the new
ground state is actually the SCF energy + energy of the STATE 1 (which is the one given as the FINAL
SINGLE POINT ENERGY is no IROOT is given). This last contribution can be either positive or negative,
depending on the case. ——ORCA手册
问题3. 我用iroot = 1，2，3，4都分别算了一遍，最终的自旋分析发现总自旋布居都是2.00，也就是说这几个态都是三重态。这是怎么回事？难道最后的波函数都是一开始的UHF波函数？
谢谢各位老师
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发表于 Post on 2023-3-30 10:54:43
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