[Pw_forum] Volume collapses when using vc-relax

[Michael Ruggiero]

Hello everybody,

After recently attending the QE workshop at Penn State, I have been trying to use QE to fully optimize organic structures. I did not have any issues trying to fully optimize oxalic acid (a small organic molecule) and its related dihydrate. However, I have been trying to get naphthalene and durene (aromatic hydrocarbons) to run but have had significant issues with decreasing volume with no vdW correction implemented. Naphthalene has a published 5 K structure, so any decrease in volume is unphysical, and I regularly see an almost 100 Ang^3 decrease in volume (~30 % decrease).

Here are all of the things I have tried:
Normconserving, US, and PAW pseudo potentials
Increasing the cutoffs to high values (up to 150/1500 Ry)
Varying the number of k-points
Various GGA functionals (PBE, PBESOL, BLYP)
Using coordinates from a 'relax'  calculation for 'vc-relax' calculations
Using optimized coordinates to do a 'vc-relax' calculation while holding volume constant ('cell_dofree=shape'), and then trying a full 'vc-relax' calculation


I am new to PW and QE, so maybe I am doing something simple incorrectly. Any insight would be greatly appreciated. I am attaching the INPUT, OUTPUT of the most recent naphthalene BLYP test, and the published CIF files for reference.

Thank you very much in advance,

Michael Ruggiero
Syracuse University Chemistry
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140630/e6e1f4db/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: INPUT_nap.in
Type: application/octet-stream
Size: 1482 bytes
Desc: INPUT_nap.in
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140630/e6e1f4db/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: nap_output.out
Type: application/octet-stream
Size: 237002 bytes
Desc: nap_output.out
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140630/e6e1f4db/attachment-0001.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: NAPHTA31.search4.cif
Type: application/octet-stream
Size: 3535 bytes
Desc: NAPHTA31.search4.cif
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140630/e6e1f4db/attachment-0002.obj>