Dear Lorenzo, Thanks for your reply. I had not considered the proton separation compared with the pseudization radius.
I do not need to calculate high energy un-occupied orbitals of H2, I was just checking my chosen pseudopotentials and other parameters on some simple gas phase molecules before I start some adsorption studies on surfaces. I will attempt my calculation with the all-electron pseudopotential you linked to and see what happens. Steven Best PhD Student, School of Chemistry and Physics, Queensland University of Technology, Brisbane, Australia ________________________________ From: users <[email protected]> on behalf of Lorenzo Paulatto <[email protected]> Sent: Wednesday, December 22, 2021 6:05 AM To: Quantum ESPRESSO users Forum <[email protected]> Subject: Re: [QE-users] Unoccupied molecular orbitals near the vacuum level. Dear Steven, Any pseudopotential (and PAW is no different) will eventually fail for sufficiently high energy. In the specific case of H2, it is worst because the two protons are closer than the typical pseudization radius. I would bet that generating a hard pseudopotential with a couple of high energy projectors could solve the problem, but I have no proof. Also the "all-electron" pseudopotential available here should work (beware, it requires a cutoff of 500+ Ry) http://quantum-espresso.org/upf_files/H.coulomb-ae.UPF<https://urldefense.com/v3/__http://quantum-espresso.org/upf_files/H.coulomb-ae.UPF__;!!NVzLfOphnbDXSw!RNcP52_WIFjau2sC7gx0qofDjhmmgaoBPgbUzG-OS-H_bR6ZkTxdKExOgUnaqP7YBnuaEgal$> -- Lorenzo Paulatto On Tue, Dec 21, 2021, 09:06 Steven Best <[email protected]<mailto:[email protected]>> wrote: I have used PWSCF v6.3 and optimized the geometry of an isolated H2 molecule in a 24 Angstrom box. I have then used pp.x to plot the occupied and un-occupied molecular orbitals. With nbnd=2 chosen for the scf calculation I obtain energy bands of: -10.3337 0.1108 eV occupation numbers 1.0000 0.0000 With nbnd=4 chosen I obtain energy bands of: -10.3343 -0.0797 0.1110 0.1375 eV occupation numbers 1.0000 0.0000 0.0000 0.0000 With nbnd=2 the plots of the occupied and unoccupied molecular orbitals look like the expected bonding and anti-bonding H2 molecular orbitals. However, if nbnd=4 is chosen, an unoccupied orbital (band 2) with a shape consisting of a number of shells is located below the anti-bonding unoccupied orbital (band 3). And another orbital with a similar shell structure (band 4) is located above the anti-bonding orbital which appears to have the opposite phase to band 2. I have calculated the vacuum level energy far away from the molecule to be approximately 0.003 eV by plotting the average potential. I think that the shape of the orbitals for nbnd=4 is possibly a result of a limitation in the plane wave method that occurs for unoccupied orbitals with an energy greater than or close to the vacuum level? Can anybody provide some insight into this behaviour? Kind regards, Steven Best PhD Student, School of Chemistry and Physics, Queensland University of Technology, Brisbane, Australia Below are my script files. ####################################################################################### # H2 molecule with nbnd = 2. &CONTROL calculation = 'scf', verbosity = 'high', restart_mode = 'from_scratch', wf_collect = .T., nstep = 200, tstress = .true., tprnfor = .true., outdir = './', prefix = 'SCF_H2_molecule_nbnd_2_t007', etot_conv_thr = 1.0d-6, forc_conv_thr = 1.0d-5, pseudo_dir = './pseudo' / &SYSTEM ibrav = 1, A = 24.0, nat = 2, ntyp = 1, nbnd = 2, ecutwfc = 60.0, ecutrho = 480.0 / &ELECTRONS electron_maxstep = 100, conv_thr = 1.0d-8, mixing_mode = 'plain', mixing_beta = 0.4, mixing_ndim = 8, diagonalization = 'david' / ATOMIC_SPECIES H 1.008 H.pbe-kjpaw_psl.1.0.0.UPF ATOMIC_POSITIONS (angstrom) H 12.00 12.00 12.00 0 0 0 H 12.750482666 12.00 12.00 K_POINTS (gamma) ####################################################################################### # Post processing for H2 molecular orbitals. # Number of bands = 2. &INPUTPP prefix = 'SCF_H2_molecule_nbnd_2_t007', outdir = './', filplot = 'H2_molecule_nbnd_2_wfc_t007', plot_num = 7, kpoint(1) = 1, kband(1) = 1, kband(2) = 2, lsign=.true. / &PLOT nfile = 1, filepp(1) = 'H2_molecule_nbnd_2_wfc_t007', weight(1)=1.0, iflag = 3, output_format = 6, fileout = '.cube' / ####################################################################################### _______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu<https://urldefense.com/v3/__http://www.max-centre.eu__;!!NVzLfOphnbDXSw!RNcP52_WIFjau2sC7gx0qofDjhmmgaoBPgbUzG-OS-H_bR6ZkTxdKExOgUnaqP7YBrc1jEos$>) users mailing list [email protected]<mailto:[email protected]> https://lists.quantum-espresso.org/mailman/listinfo/users<https://urldefense.com/v3/__https://lists.quantum-espresso.org/mailman/listinfo/users__;!!NVzLfOphnbDXSw!RNcP52_WIFjau2sC7gx0qofDjhmmgaoBPgbUzG-OS-H_bR6ZkTxdKExOgUnaqP7YBvfx8FKz$>
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