Dear all,

I am trying to verify the spin selection for the hydrogen combustion system with the wB97M-V method. For example, I choose three ways to calculate the energy with the wB97M-V method and cc-pVTZ basis set: spin=1, spin=3, and guess=mix, and the lowest energy was chosen to draw the dissociation curve. The dissociation curve is not smooth. Here is one input of my input files:

spin =1 or 3:

$molecules

0 1(3)

O 11.9573 7.97905 12.3234

O 12.4226 6.78293 12.3816

$end

$rem

JOBTYPE FORCE

MEM_TOTAL 24000

METHOD wB97M-V

BASIS cc-pVTZ

UNRESTRICTED true

SYMMETRY false

SYM_IGNORE true

$end

guess=mix:

$molecules

0 1

O 11.9573 7.97905 12.3234

O 12.4226 6.78293 12.3816

$end

$rem

JOBTYPE FORCE

MEM_TOTAL 24000

METHOD wB97M-V

BASIS cc-pVTZ

UNRESTRICTED true

SYMMETRY false

SYM_IGNORE true

SCF_GUESS gwh

SCF_GUESS_MIX 2

$end

Here is the oxygen dissociation lcurve:

After that, I adopted the INTERNAL_STABILITY = TRUE in my input to perform internal stability analysis and generate the corrected MOs. But the SCF failed to converge.

Can someone explain why is this happening? Is this keyword( INTERNAL_STABILITY) equivalent to stable=opt in Gaussian?

Thanks a lot!