Dear Psi4 users,

I am having trouble running some larger CCSD optimization; they die without any helpful hints in CCDENSITY.

I am running these optimizations on a dual Intel E5-2650 v2 server with 96 GB RAM. I am requesting up to 80 GB of RAM in the input and I have plenty of disk space. I am the only user running QM jobs. I have tried different physical scratch disks with the same effect so it is not bad disk, and I don’t think it is bad RAM either. Pretty much every smaller CCSD optimization completes OK. I have tried "Psi4 0.4.16 Driver"and “Psi4 0.4.131 Driver” from miniconda installs.

One particular example is cyclopropane cation in Cs symmetry. An all-electron CCSD/aug-cc-pVTZ optimization with 299 basis functions (in Cs symmetry) generates 27 GB of <ab|cd> integrals and runs happily. An all-electron CCSD/aug-cc-pwCVTZ calculation of the same structure with 338 basis functions generates 45 GB of <ab|cd> integrals and stops in CCDENSITY in the first round of geometry optimization. The last lines of output are:

```
Energies re-computed from CC density:
-------------------------------------
One-electron energy = 0.733757964839662
IJKL energy = 0.108645022149429
IJKA energy = -0.001566176800092
IJAB energy = -1.348802966570895
IBJA energy = -0.336343664069401
CIAB energy = -0.005935039502245
```

and I find in dmesg output: psi4[18277]: segfault at 7f9814728020 ip 0000000006d62547 sp 00007ffdda9bdd18 error 6 in psi4[400000+74f3000]. The most recently accessed file in my scratch directory is either .77 or .107

The same thing happens with oxetane in Cs geometry (input given below) where 35 GB of <ab|cd> integrals is generated using 322 basis functions. When I am running even larger calculations (like protonated methyloxirane in C1) where 397 basis functions give 169 GB of <ab|cd> integrals, Psi4 nicely tells me that there is no memory left in the beginning of CCDENSITY.

I am suspecting that I am trying to do a calculation that does not fit into 80 GB memory limit but I am perplexed because (i) there are no complaints from Psi4 about the lack of memory, and (ii) I am able to carry out the same CCSD optimizations with much less memory using another commonly used QM program.

Any words of wisdom about how to carry out Psi4 CCSD optimizations that generate up to 45 GB of <ab|cd> integrals on a machine with 96 GB of RAM?

Thank you!

Kalju

## Sample input:

# Oxetane Cs optimization

memory 80 gb

molecule oxetane {

0 1

C 0.000000 -1.067499 -0.067639

C -1.026596 0.059978 0.071429

C 1.026596 0.059978 0.071429

O 0.000000 1.065292 -0.105166

H 0.000000 -1.836963 0.696861

H 0.000000 -1.522356 -1.052531

H -1.799186 0.136630 -0.689767

H -1.476526 0.131350 1.062616

H 1.476526 0.131350 1.062616

H 1.799186 0.136630 -0.689767

}

set globals {

basis aug-cc-pVTZ

freeze_core false

molden_write true

}

set scf {

E_Convergence 1.0e-09

D_Convergence 1.0e-08

}

set ccenergy {

cc_num_threads 6

R_Convergence 5.0e-08

}

set cclambda {

R_Convergence 5.0e-08

}

set optking {

G_Convergence GAU_TIGHT

}

optimize(‘ccsd’)