[CP2K-user] [CP2K:17901] understanding BSSE print out

[Krack Matthias (PSI)]

Hi Victor

Without the full input, it is difficult to make any suggestion. Do you have a &BSSE section defining the FRAGMENTS?

Best

Matthias

From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Victor Volkov <volkovskr at gmail.com>
Date: Saturday, 15 October 2022 at 19:53
To: cp2k <cp2k at googlegroups.com>
Subject: [CP2K:17873] understanding BSSE print out
Dear members:
good evening/morning.

it is not clear to me how to interpret CP2K print out for BSSE.

If I take a small guest (like benzene) next to a carbon layer using GWP/PBE/DZVP
Of course, since interactions are so week, DFTD3 is a must - otherwise a benzene may "fly away".

Then, using BSSE  for S1(guest) and S2 (carbon layer)
CP2K prints
S1 + S2ghost: Total energy -455.12112693238430 Hartree
S1ghost + S2: Total energy -455.12112693238430 Hartree
S1           + S2: Total energy -455.12112693238441 Hartree

The differences are none or tiny.

However, the final print is:
CP-corrected Total energy:        0.015729
1-body contribution:                 -44.96634268204556
1-body contribution:                -410.13905550190344
2-body contribution:                 455.121127
BSSE-free interaction energy:      455.121127

First, it is not clear what is "CP".

Next, if this is the value of the BSSE artifact (due to the wave-function truncation),
then its huge 41.2964895 kJ/mole.
This would be almost twice larger than the binding energy of benzene-like guests when at carbonaceous surfaces.
This would mean that quality evaluations of binding energies for such systems using CP2K would be very difficult.

Any comments to hear would be nice.

Finally, it is not clear why 2-body contribution and BSSE-free interaction are printed as positive numbers.

I hope the questions I ask be interesting for users and helpful for the on-line manual to update.

After all, I wish to note that it was by a rare chance I was able to track the old
notice on the importance of declaring
    &KIND X_ghost
     BASIS_SET DZVP-MOLOPT-SR-GTH
     GHOST
    &END KIND

Even though ...
if I skip such definition, the numbers would come "a bit better"
:-)
CP would be about 21 kJ/mole, what is about comparable to the binding energy
of a benzene-like guest to a carbonaceous material.

Thank you for your time and attention.

I wish everybody be well and happy.

Victor






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