Frequently Asked Questions
**************************

* General questions, licensing

  * Is VASP included with AMS?

  * Are all VASP features supported?

  * How do I convert my old VASP inputs (up to AMS2025) to the new
    AMS2026 format?

  * The program is always running in serial (using 1 core) ?

* Issues


General questions, licensing
============================


Is VASP included with AMS?
--------------------------

No, you need to provide your own VASP binary and license.


Are all VASP features supported?
--------------------------------

No, only some common features as detailed in this manual are supported
by the AMS interface.


How do I convert my old VASP inputs (up to AMS2025) to the new AMS2026 format?
------------------------------------------------------------------------------

AMSinput attempts to convert some of the input options, but there is
no guarantee that it does so correctly. Double-check the input options
carefully.


The program is always running in serial (using 1 core) ?
--------------------------------------------------------

When running VASP through AMS, you need to set the environment
variable "SCM_DISABLE_MPI=1". This causes AMS to launch in serial and
you will see a line like this at the top:

   AMS 2024.101  RunTime: Apr10-2024 06:40:44  ShM Nodes: 1  Procs: 1

This is expected and intended. This line does **not** mean that VASP
is running in serial.

At the top of "VASP.log" we can find more information about how many
cores VASP is using:

   running    4 mpi-ranks, on    1 nodes
   distrk:  each k-point on    4 cores,    1 groups
   distr:  one band on    1 cores,    4 groups
   vasp.6.4.3 19Mar24 (build Oct  2 2025 12:09:38) complex

In this case, we see that VASP is actually running on 4 processor
cores.

You can also monitor the CPU usage using "top" or other utilities.


Issues
======

With old versions of VASP (VASP 6.3 or older), Engine VASP
automatically restarts the VASP process with a new plane wave basis
set ("ISTART=0", "LWAVE=.FALSE.") when a change in the lattice is
detected. This is done to prevent buildup of Pulay stress.
Additionally, for certain calculations this may result in an overall
speedup since there is no unnecessary writing of the "WAVECAR".
