I am calculating a single point energy of a triplet spin state in quintet geometry. Despite increasing the number of cycles in SCF, the single-point calculation is not converging. Please help me out.
It is showing this error:
>>>>>>>>>> Convergence criterion not met.
SCF Done: E(UTPSSh) = -2245.15879974 A.U. after 2049 cycles
NFock=*** Conv=0.12D-05 -V/T= 2.0029
= 0.0000 = 0.0000 = 1.0000 = 2.0285 S= 1.0095
= 0.000000000000E+00
KE= 2.238627472276D+03 PE=-9.853763435892D+03 EE= 3.112362544981D+03
Annihilation of the first spin contaminant:
S**2 before annihilation 2.0285, after 2.0003
Convergence failure -- run terminated.
Error termination via Lnk1e in /home/app/gaussian/g09/l502.exe at Fri Jan 13 09:22:27 2023.
Job cpu time: 12 days 19 hours 10 minutes 36.9 seconds.
The standard solution in such cases is to use a simpler method and/or a basis set to get a good starting guess. Try to calculate HF/3-21G or, in your case, you can try to calculate the singlet, then save the chk-file and use the option guess=read when calculating the target system.
If the proposed method does not help, then it is worth thinking about the possibility of the existence of the system in such a state or the possibility of carrying out such calculations in this approximation.
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