I tried to do MECP, but i faced a problem, Key ‘hf/nossa’ is not known. Here I attached my input file here.

$molecule

0 3

N

N 1 B1

O 1 B2 2 A1

O 3 B3 1 A2 2 D1 0

B1 1.14416032

B2 1.32890525

B3 1.61898088

A1 144.25929376

A2 116.15338594

D1 0.02930681

$end

$rem

JOBTYPE opt

MECP_OPT true

MECP_METHODS mecp_direct

METHOD ccsd

BASIS aug-cc-pvtz

XOPT_STATE_1 [1,0]

XOPT_STATE_2 [0,1]

GEOM_OPT_TOL_GRADIENT 30

$end

I ran this with Q-Chem 6.0.1 and it dies in first CCSD calculation due to insufficient memory, here is the message:

```
Insufficient memory for integral transformation.
Minimum contiguous memory block required: 700 MB
Largest contiguous memory block available from CC_MEMORY: 513 MB
Largest contiguous memory block outside CC_MEMORY: 192 MB
Please either increase CC_MEMORY to at least 2052
or increase MEM_TOTAL to at least 2508
Q-Chem fatal error occurred in module liblegacy/liblegacy/qcimport_motran_qints.C, line 1191:
AO-MO integral transformation failed
```

Resolution seems pretty straightforward.

I tried with TOT_MEM=50000 but same error showed.

With larger MEM_TOTAL, the CCSD energy calculation runs and I can reproduce your error. The message

```
Entering direct/semidirect transformation code...
The following integrals will be calculated:
(11|11)
```

The error message that you note is indeed cryptic, but th position in the code suggests to me that perhaps AO2MO_DISK needs to be increased for the semidirect integral transformation. I also suggest that you should not start a calculation like this, for the first time, in a sizable basis set such as aug-cc-pVTZ. Use something small like 6-31G* in order to get your bearings.