Such a technique/code has not existed yet.

Thanks, Jun Lin, for your answer.

So far, I concern that if I can find a way to determine the "Magnetic Field, B, at the flare site by using extrapolation with taking assistance of PFSS (potential field source surface), it would be helpful determine the possible volume of the energy of the flare.

One can directly measure the magnetic field in the photosphere only so far. Measurement of that in the chromosphere is not very reliable, and no way to measure the magnetic field in the corona so far. PFSS can only give a rough description of the related magnetic field, NLFFF approach is still an open question.

http://adsabs.harvard.edu/abs/2005A%26A...433.1133K

You may find this paper useful.

Thanks for the paper.

Some of our colleagues (e.g., Y. P. Li, W. Q. Gan, L. Feng) made two works too that showed that HXR source can be used to determine the possible amount of the energy for a flare, and this paper which you referred will also be helpful.

Make use of Spectral observational data in different wave-band (including Visible light, Infred light, ultraviolet, X-ray, gama-ray ect.), with the spectral diagnosis method and the spectral profile analysis, it is possible to measure these physical parameters mentioned above. It is a possible way.

Thank you very much, Dr. Xiao-Ma Gu

I would also add an insight about magnetic topology in a flare by going through transport models for particles, and then simulating emission profiles at different levels using warm/cold target models (assumption depends on event timing), then you can have a bracket value for total spatial energy release distribution, and its categorization. The CME observations with known models can also give you an approximate estimation of the kinetic energy involved. The hard part of this is to understand the energetic processes involved on or around reconnection regions.