Numerical problems with relativistic zora calculations

[moritzgubler]

Hi

I recently noticed, that I am not able to converge zora calculations with tight precisions. The problem is the following: consider the input file

world_prec = 1.0e-6
world_unit = angstrom
WaveFunction {
  method = lda
  relativity = zora
}
Molecule {
$coords
H 0.0 0.0 0.0
H 0.9 0.0 0.0
$end
}

This does not converge. It is close though, it almost reaches the threshold after 10 SCF iterations. After that the MO residual stays slightly above the convergence threshold for the next 20 SCF iteration. Then the simulation goes really wrong and the residual starts to diverge. Also, the memory required by mrchem continuously grows and after 47 iterations i stopped the program because it used up the entire memory of my workstation (32 GB).

I used the newest version of mrchem and tested the functionals lda, pbe and pbe0 where the problem is the same. It is also present in all the other molecules I tested: H_2O, NH_4, it is even more severe in the NH_4 molecule. When the world_prec is increased to 1e-4 or the zora method is not used, the calculation converges. Below you find the output of the SCF cycle from the input file from above.

I tried to play around with some SCF keywords to get these calculations to converge, but was not able to do so. Do you have an idea what could go wrong here? Thanks a lot for looking into this.

===========================================================================
 Iter           MO residual             Total energy                Update
---------------------------------------------------------------------------
    0          1.000000e+00          -1.126549655620         -1.126550e+00
    1          5.588320e-02          -1.137476166839         -1.092651e-02
    2          5.683084e-03          -1.137719316527         -2.431497e-04
    3          1.426500e-03          -1.137732864726         -1.354820e-05
    4          8.197909e-04          -1.137724341320          8.523405e-06
    5          7.077225e-04          -1.137733969255         -9.627935e-06
    6          5.908577e-05          -1.137733876118          9.313768e-08
    7          6.918668e-05          -1.137733974038         -9.792065e-08
    8          3.802536e-05          -1.137733939618          3.442023e-08
    9          4.411585e-05          -1.137733973516         -3.389800e-08
   10          2.451983e-05          -1.137733968648          4.867959e-09
   11          4.849671e-05          -1.137733930095          3.855352e-08
   12          5.043205e-05          -1.137733966139         -3.604488e-08
   13          2.160990e-05          -1.137733974271         -8.131049e-09
   14          5.883780e-05          -1.137733878856          9.541477e-08
   15          6.316945e-05          -1.137733974749         -9.589299e-08
   16          1.297690e-05          -1.137733971889          2.859604e-09
   17          3.504807e-05          -1.137733951260          2.062898e-08
   18          3.231851e-05          -1.137733973203         -2.194333e-08
   19          1.141251e-05          -1.137733973642         -4.380603e-10
   20          1.059654e-05          -1.137733974027         -3.849538e-10
   21          1.189108e-05          -1.137733971784          2.242024e-09
   22          2.156554e-05          -1.137733970533          1.251466e-09
   23          2.344845e-05          -1.137733967163          3.370509e-09
   24          3.120666e-05          -1.137733957546          9.616949e-09
   25          3.934829e-05          -1.137733952101          5.444069e-09
   26          3.975666e-05          -1.137733953968         -1.866136e-09
   27          5.046707e-05          -1.137733923887          3.008081e-08
   28          6.774338e-05          -1.137733892736          3.115061e-08
   29          9.342978e-05          -1.137733801676          9.106051e-08
   30          1.294986e-04          -1.137733711446          9.023012e-08
   31          1.567931e-04          -1.137733572297          1.391487e-07
   32          1.830440e-04          -1.137733321878          2.504186e-07
   33          2.267721e-04          -1.137732863967          4.579118e-07
   34          3.672284e-04          -1.137730986239          1.877727e-06
   35          5.095956e-04          -1.137730116688          8.695510e-07
   36          5.585423e-04          -1.137728828327          1.288361e-06
   37          6.677414e-04          -1.137724757660          4.070667e-06
   38          9.842135e-04          -1.137711255339          1.350232e-05
   39          1.440041e-03          -1.137693119222          1.813612e-05
   40          1.688429e-03          -1.137696282315         -3.163093e-06
   41          1.908598e-03          -1.137656400602          3.988171e-05
   42          3.059050e-03          -1.137439252897          2.171477e-04
   43          4.264359e-03          -1.137195631600          2.436213e-04
   44          4.850040e-03          -1.136858487554          3.371440e-04
   45          5.472838e-03          -1.135977026135          8.814614e-04
   46          8.564126e-03          -1.128026930496          7.950096e-03
   47          1.256601e-02          -1.125935204092          2.091726e-03