Hi,

At our computational facility we have a user whose geometry optimization exhibits persistent imaginary modes. I have a script to iteratively displace the geometry along the imaginary mode and reoptimize (which I’m happy to share if it’s of interest to others), and the opt+freq cycle continues indefinitely. Gas-phase optimization works fine. I’ve tried changing xc_grid, and separately changing every relevant CPCM keyword:

SwitchThresh to 12

SASradius to 0.05

SurfaceType to SES

HPoints 302 and HeavyPoints 590,

all with the same outcome. I’ve tried reducing GEOM_OPT_TOL_GRADIENT to 3, which has the same result; here are the final energies of the optimizations:

ropt5_iter_10.out: **Final energy** is -759.095968138437

ropt5_iter_11.out: **Final energy** is -759.095966551625

ropt5_iter_12.out: **Final energy** is -759.095967984947

ropt5_iter_13.out: **Final energy** is -759.095966394464

ropt5_iter_14.out: **Final energy** is -759.095967838025

ropt5_iter_15.out: **Final energy** is -759.095966250109

ropt5_iter_1.out: **Final energy** is -759.095967228929

ropt5_iter_2.out: **Final energy** is -759.095968663064

ropt5_iter_3.out: **Final energy** is -759.095967107375

ropt5_iter_4.out: **Final energy** is -759.095968544787

ropt5_iter_5.out: **Final energy** is -759.095966979221

ropt5_iter_6.out: **Final energy** is -759.095968414041

ropt5_iter_7.out: **Final energy** is -759.095966843379

ropt5_iter_8.out: **Final energy** is -759.095968280314

ropt5_iter_9.out: **Final energy** is -759.095966700833

At one point I was thinking the problem is limited to the freq calulation, but these energy variations, although small, but considering the tight convergence tolerance, suggest that the problem possibly extends to the CPCM gradients as well.

I see a similar problem has been discussed previously: Imaginary frequency in CPCM solvent. So it appears the problem is still present in new versions (I’m using 6.02).

Here’s an example input file:

$molecule

-1 1

C -3.15855 2.38634 -0.145622

C -2.47795 1.06058 -0.371107

O -1.14541 1.17615 -0.189907

O -3.04181 0.0267281 -0.676997

C -0.341712 -0.0272315 -0.238338

C 0.912436 0.289266 -1.06424

C 1.81806 1.3372 -0.501815

N 2.96214 1.03343 0.0945355

O 3.76283 1.94341 0.523864

O 3.31118 -0.224597 0.269313

C -0.162378 -0.488376 1.22216

N 1.03208 -1.00047 1.56233

O -1.12867 -0.433838 1.9969

C 1.25944 -1.47831 2.91831

H -2.63465 3.18215 -0.681251

H -4.19719 2.33053 -0.471105

H -3.12401 2.62704 0.922086

H -0.926312 -0.804251 -0.741514

H 1.47584 -0.637634 -1.20484

H 0.551382 0.599781 -2.05315

H 1.60363 2.39369 -0.584651

H 1.8759 -0.831314 0.980104

H 2.29522 -1.81404 2.99421

H 1.08537 -0.689666 3.66052

H 0.595334 -2.31606 3.15661

$end

$rem

JOBTYPE = opt

BASIS = 6-31G**

METHOD = B3LYP

DFT_D = D3

SCF_ALGORITHM = DIIS_GDM

SOLVENT_METHOD = PCM

SYMMETRY = FALSE

SYM_IGNORE = TRUE

MEM_TOTAL = 8000

$end

$pcm

THEORY CPCM

METHOD SWIG

Radii BONDI

$end

Any suggestions will be appreciated, thanks.