Dear users, I am running a simple 2-atomic non-magnetic (NM) bcc Cr system (see below for the input file) with v.4.2.1 and I keep getting an error message regarding a negative dr2:
from mix_rho : error # 1 negative dr2 This error occurs for values close to as well as away from the estimated equilibrium volume. What is the possible the origins of this error and how may I eliminate it? I have tried to change the mixing_beta in the range 0.1 to 0.8, as well as changing the mixing mode to 'TF'. I have also tried to set nspin = 2 with a zero start magnetisation since an anti-ferromagnetic (AFM) start configuration does not give rise to the problem (but yields the AFM solution instead of the NM one). However. this also gives the error. Finally, I tested to use ibrav = 3 and with only one atom in the cell, but I still get the above error. What I have noticed is that in the AFM case I get a couple of very flat bands in the bandstructure just above the Fermi level. If I change to a USPP potential or an alternative PAW potential these bands disappear, and the above error does not occur. Can the potential I use in the present case be the source to the error, and if yes, what is the reason behind it? I would appreciate any help or suggestions. Dan %------------------------------------- &CONTROL calculation = 'scf', restart_mode = 'from_scratch', prefix = 'Cr', tstress = .true., tprnfor = .true., pseudo_dir = '/home/forsdan/PROGRAMS/QUANTUM_ESPRESSO/espresso-4.2.1_intel/pseudo/', outdir = '/home/forsdan/FeCr_PROJECT/TEMP_PAW/' / &SYSTEM ibrav = 1, celldm(1) = 5.378798, nat = 2, ntyp = 1, ecutwfc = 40.0, ecutrho = 180.0, nbnd = 14 occupations = 'smearing', smearing = 'mp', degauss = 0.022, nspin = 1, / &ELECTRONS electron_maxstep = 100, conv_thr = 1.0d-8, diagonalization = 'cg', mixing_mode = 'plain', mixing_beta = 0.3 / ATOMIC_SPECIES Cr 51.996 Cr.pbe-paw_kj_6.UPF ATOMIC_POSITIONS {crystal} Cr 0.00 0.00 0.00 Cr 0.50 0.50 0.50 K_POINTS {automatic} 12 12 12 0 0 0 %-------------------------------------