Hello, guys.

Recently I run SP calculation using ADC(2)-s but it doesn’t work well after finishing SCF calculation.

This is the input file.

```
$rem
JOBTYPE = SP
METHOD = ADC(2)
BASIS = 6-31G*
DFT_D = EMPIRICAL_GRIMME
SYMMETRY = FALSE
SYM_IGNORE = TRUE
CC_SYMMETRY = FALSE
EE_SINGLETS = 3
MAX_SCF_CYCLES = 512
SCF_CONVERGENCE = 10
THRESH = 14
MEM_TOTAL = 192000
MEM_STATIC = 2000
$end
$empirical_dispersion
s6 1.00
$end
```

And the error message looks like it.

```
Q-Chem fatal error occurred in module libmdc/newfileman.C, line 384:
FileMan error: Error writing 425984 bytes to file FILE_HALF_TRNS1
Path: /work/116310.dinger00/qchem202633/65.121
Please submit a crash report at q-chem.com/reporter
```

If there is anyone to know how to solve this problem, can you give me an advice?

In addition, I found the difference of EE_STATES and EE_SINGLETS and Q-chem manual indicates that EE_STATES is for the open-shell or unrestricted closed-shell calculations and EE_SINGLETS is for the restricted closed-shell calculations. I’d like to calculate S1 state energy from S0 optimized structure. S1 state is open-shell system(there is one unpaired electron), as you know, then should I choose EE_STATES option? If I turn on EE_SINGLETS instead of EE_STATES, what is happened?

Moreover, Unrestricted means the separation of the orbital of alpha electron and beta electron. I know this concept but don’t know well when Unrestricted turn on or off exactly. can you explain it through some examples?

Thank you in advance.