Many many thanks for your perfect comments and valuable guidance.

Saeed

JK and COSX are two ways of accelerating calculation of HF exchange, the former requires auxiliary basis set of JK type. Without RIJCOSX, the HF exchange will be calculated without any approximation.

Thank you very very much.
When the "RIJK" is removed, the calculations runs and terminates normally.
It seems calculations successfully runs also without the "RIJCOSX". Is there any difference between existence or the lack of presence "RIJCOSX"?

Saeed

Just avoid using RIJK (using RIJCOSX instead)

Dear Tian,

If possible and you kindly let me, I am going to respectfully ask you a short question. Please let me know what is wrong in the below orca input so this calculation is immediately broken:

! DLPNO-CCSD(T) tightPNO RIJK aug-cc-pVTZ aug-cc-pVTZ/JK aug-cc-pVTZ/C tightSCF noautostart miniprint nopop
%maxcore     6000
%pal nprocs   8 end

%basis
NewGTO I "aug-cc-pVTZ-PP" end
NewECP I "SK-MCDHF-RSC" end
NewAuxCGTO I "aug-cc-pVTZ-PP/C" end
end

* xyz   0   1
F      0.00000000    0.00000000    2.31701469
I      0.00000000    0.00000000    0.36278221
N     -0.00000000    0.00000000   -2.21522715
C      0.00000000    0.00000000   -3.35805455
H      0.00000000    0.00000000   -4.42567175
*

The error message:

               *****************************************************************
               ** There are no AuxJK  basis functions on atom number   1 (I ) **
               *****************************************************************
[file orca_main/maininp2.cpp, line 2444]:    The basis set was either not assigned or not available for this element - Aborting the run

In advance, too many thanks for your kind attention.

Sincerely,
Saeed