Error and Warning Messages#

Last update: 2026-01-30

ARPACK and ARPACK-INVERSE#

WARNING: Linear solver residual of ARPACK-INVERSE set too large in multiband quantum solver#

Linear solver residual of ARPACK-INVERSE set too large in multiband quantum solver. ARPACK-INV solver uses internally the linear solver on each iteration, therefore the accuracy of ARPACK-INV is limited by accuracy of the linear solver. It is recommended to set the residuals of linear solver to be smaller than residuals of the ARPACK-INV, otherwise this warning is thrown. The residual of the ARPACK-INV can be set by a keyword arpack_inv{ accuracy }. The linear solver residuals can be set by keywords arpack_inv{ linear_solver{ abs_accuracy } } or arpack_inv{ linear_solver{ rel_accuracy } }.

ERROR: maximum number of iterations exceeded.#

With this error the LOG file claims that the ARPACK reached the maximum number of iterations before it converged to solutions with requested residuals.

How to proceed:

  1. Set debuglevel to 2 to get more useful output in the LOG file once it actually converges; It may be useful when you contact us with this simulation lated.

  2. Increase the number of iterations to give the ARPACK more time to converge

  3. Consider increasing number of states included in the calculation. Note that it will inflate time needed for ARPACK to converge.

  4. Try changing the preconditioner to make the ARPACK finding the solutions quicker.

Exit codes#

nextnano++ exit code: -1073741795#

Simulation *.log file contains the following exit code -1073741795 or other big negative number

(nextnano++ exit code: -1073741795)

Most likely you need to install the Microsoft Visual C++ Redistributable . Choose the corresponding version matching your operation system architecture (most likely X64) from the section Latest Microsoft Visual C++ Redistributable Version. It’s a typical error when running nextnano++ on Windows Server OS.

It is also possible that your CPU is not suited for nextnano++ executable, i.e., you are using processor from Pentium family, typical on old laptops. You can use nextnano++_Microsoft_32bit_serial.exe, see FAQ of nextnanomat.

Other possibility is that your computer enters sleep mode during the runtime of your simulation. Turn off disable sleep mode on your computer to fix the problem.

nextnano++ exit code: -1#

Simulation *.log file contains the following exit code -1

(nextnano++ exit code: -1)

It means that the simulation has been aborted by nextnanomat or by other means.

nextnano++ exit code: 1#

Simulation *.log file contains the following exit code 1

(nextnano++ exit code: 1)

It means that there is error in the command line calling the solver.

nextnano++ exit code: 3#

Simulation *.log file contains the following exit code 3

(nextnano++ exit code: 3)

There is a problem with validating your license.

Other#

Error: (nodes number of coordinate 1) != (lines number in file)#

Simulation *.log file contains the following error

error:(nodes number of coordinate 1) != (lines number in file)

It means that you have defined values at some grid points twice inside the imported file. Check if some points are duplicated in the file that you are trying to import. For example, you should avoid situation as the following:

…
1.0    0.5
1.1    0.5
1.2    0.5
1.2    0.6
1.3    0.6
…

In this case the point 1.2 is defined twice, which is the source of the problem.