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# 3.11. Dump styles

Classes that dump per-atom info to files are derived from the Dump class. To dump new quantities or in a new format, a new derived dump class can be added, but it is typically simpler to modify the DumpCustom class contained in the dump_custom.cpp file.

Dump_atom.cpp is a simple example of a derived dump class.

Here is a brief description of methods you define in your new derived class. See dump.h for details.

write_header | write the header section of a snapshot of atoms
count | count the number of lines a processor will output
pack | pack a proc’s output data into a buffer
write_data | write a proc’s data to a file
modify_param | called when dump_modify is executed (optional)
extract | provide access to internal data (optional)

See the dump command and its custom style for a list of keywords for atom information that can already be dumped by DumpCustom. It includes options to dump per-atom info from Compute classes, so adding a new derived Compute class is one way to calculate new quantities to dump.

Note that new keywords for atom properties are not typically added to the dump custom command. Instead they are added to the compute property/atom command.