=head1 B<ESPT Programming Conventions>

=head1 B<============================>

=over 5

=item Atoms:

All atoms are stored as atomic symbols.  If the atomic number is required
use the atomconvert method at that time.

=item Energies:

In fchk files, always use Total energy as the EELEC.

=item File contents:

Each ESS file is assumed to contain the results from only one calculation
unless the calculation was an Opt Freq run.

=item Pragmas:

All ESPT objects must conform to the use strict and use warnings pragmas.

=item Loops & counters:

Use scalar(@array) or $#array rather than counters when at all possible.
If a counter must be employed use the generic $counter rather than creating
a new variable.

=item MO Occupations

All MO occupations are stored as 0, 1, 2, or a real number for fractional
values.  Conversion to more chemical values such as "Occ." or "Virt."
should be done elsewhere.  

=item Object data:

Each ESPT object is a Hash. Each Hash key should contain either a scalar 
value or a tensor of scalar values.  Hashes of Hashes should be avoided
as this requires significant modification to the get routine.

=item Units:

All values are stored internally in atomic units with the exception of 
coordinates, which are stored in angstroms. Unit conversion should be 
done in the program employing ESPT modules.

=back

=cut