[QE-users] S matrix not positive - MgH2 system

[RAQUEL YANES RODRIGUEZ]

Dear Quantum Espresso users,

I’m trying to run a simple SCF calculation for a MgH₂ structure using  
Quantum ESPRESSO, but I keep encountering an "S matrix not positive  
definite" error. I’ve attempted several modifications to the input,  
but none have resolved the issue:

- Increase Ecutwfc and Ecutrho values
- Increase number of k-points
- Change the pseudopotential
- Change from ibrav=6 to ibrav=0

I suspect that the problem might be related to the geometry of the  
structure, though it should be correct since it’s a well-known system.

The input i'm using is the following one:

---------------------------------------------------------------------------------------------
&CONTROL
title = 'MgH2' ,
calculation = 'scf' ,
outdir = './' ,
pseudo_dir = './' ,
/
&SYSTEM
ibrav = 6,
A = 4.48 ,
C = 2.99 ,
nat = 15,
ntyp = 2,
ecutwfc = 90 ,
ecutrho = 400 ,
input_dft = 'PBE'
occupations = 'smearing'
smearing = 'gaussian'
degauss = 0.02
/
&ELECTRONS
conv_thr = 1.0d-8
/
&IONS
/
ATOMIC_SPECIES
Mg 24.3050 Mg.pbe-spnl-kjpaw_psl.1.0.0.UPF
H 1.00000 H.pbe-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS angstrom
Mg 0.000000 0.000000 0.000000
Mg 0.000000 0.000000 2.992537
Mg 0.000000 4.476694 0.000000
Mg 0.000000 4.476694 2.992537
Mg 4.476694 0.000000 0.000000
Mg 4.476694 0.000000 2.992537
Mg 4.476694 4.476694 0.000000
Mg 4.476694 4.476694 2.992537
Mg 2.238347 2.238347 1.496269
H 0.875516 3.601178 1.496269
H 3.601178 0.875516 1.496269
H 3.113863 3.113863 0.000000
H 3.113863 3.113863 2.992537
H 1.362831 1.362831 0.000000
H 1.362831 1.362831 2.992537
K_POINTS automatic
4 4 4 1 1 1
---------------------------------------------------------------------------------------------

Does anyone know how to solve this problem?

Thank you in advance! :)