[CP2K:7431] Nonsense VELOCITY DCD files with the default unit bohr/au_time

[Krack Matthias (PSI)]

Hi Norman

The DCD format provides the information (coordinates, velocities, and forces) as 4 byte floating point numbers in binary format and thus the accuracy should be fine. You should just dump the 32 bit floating point numbers from the binary DCD in a proper format. Indeed, the standard floating point output using just 6 digits might not be appropriate for some cases. In principle, the DCD format is here even superior, i.e. much more compact/efficient than the usual ASCII XMOL format. I have added a –eformat flag to dumpdcd.f90 code in cp2k/tools which optionally allows the dump in scientific format (ES14.6 instead of F14.6). I hope this option will provide enough significant digits for further processing incl. velocity data.

Best

Matthias

From: cp... at googlegroups.com [mailto:cp... at googlegroups.com] On Behalf Of NORMAN GEIST
Sent: 15 February 2016 15:07
To: cp2k
Subject: [CP2K:7431] Nonsense VELOCITY DCD files with the default unit bohr/au_time

Just to warn people and to have this searchable I want to inform that using DCD VELOCITY files using the default unit bohr/au_time
does not represent a reasonable floating point range when saved to DCD format. Cause of the fixed point format obviously used. most values are zero, highest values are 0.001

Cheers

Norman Geist
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