疑问:tddft中的XASLOC，轨道局域化的含义

zhanfei

ORCA manual 5.5.2 Use of TD-DFT for the Calculation of X-ray Absorption Spectra中
第二个例子计算TiCl4中Cl原子1s轨道的激发，其中XASLoc[0] = 1,4因为1-4轨道是四个Cl的1s轨道。
manual中有一段
And looking at the energy range or the orbital composition, we nd that orbitals 1 through 4 are Cl 1s-orbitals. They
all have the same energy since they are essentially non-interacting. Hence, we can localize them without invalidating
the calculation。
之后我又去ORCA input library看到这么一段
If a molecule contains more than one atom of the XAS element and the 1s orbitals are symmetry equivalent it may be necessary to localize them first. This should only be done when necessary.

%tddft
        XASLoc[0] = 0,1 # Localizing alpha orbitals of range 0 to 1.
        XASLoc[1] = 0,1 # Localizing beta orbitals of range 0 to 1.
        .....

end


我的疑问是，为什么不localize这四个轨道（XASLoc[0] = 1,4）计算就不能成立呢（invalidating），激发轨道窗口设置成1,4为什么不可以，设置成这4个轨道都可以被单独激发？是不是和csf建立有什么关系。另外这里localize的意义是什么，和直接用其中一个，忽略其他三个有什么不同？感觉我又有些基础有缺漏了。
多谢大家，
Sincerely，

! BP86 def2-TZVP(-f) def2-TZVP/J ZORA TightSCF
%maxcore 1024
%tddft XASLoc[0] = 1,4
OrbWin[0] = 1,1,-1,-1
NRoots 25
MaxDim 150
DoQuad true
end
* int 0 1
Ti 0 0 0 0 0 0
Cl 1 2 3 2.15 0 0
Cl 1 2 3 2.15 109.4712 0
Cl 1 2 3 2.15 109.4712 120
Cl 1 2 3 2.15 109.4712 240
*