Formatted Checkpoint File

What is formatted checkpoint file?

When finishing the calculation in Gaussian, it will produce a check file (.chk). It contains all the information on electron density. To make the chk file suitable for input into a variety of visualization software, we convert it into formatted forms (.fchk).

Demonstrate: Linux system

When finishing the calculation in Gaussian, type "ls" to check the chk file had produced. Then, type "formchk filename.chk" and type "ls" to check whether the fchk file produced or not.

                        
         # Example: convert NCOHeBN-_MP2_pVDZ_180.chk into fchk file
         
         linear/fchk> ls
         OCNArBN-_MP2_pVDZ_180.chk
         linear/fchk> formchk OCNArBN-_MP2_pVDZ_180.chk
         Read checkpoint file OCNArBN-_MP2_pVDZ_180.chk type G16
         Write formatted file OCNArBN-_MP2_pVDZ_180.fchk
         FChkPn:  Initial coordinates match /B/.
         linear/fchk> ls
         OCNArBN-_MP2_pVDZ_180.chk  OCNArBN-_MP2_pVDZ_180.fchk
         linear/fchk>

Reference

電子密度圖簡易教學 (slides from 昱瑋學長)
如何用 Gaussian 計算及繪製電子密度?
Gaussian: formchk