Restart calculation using .fchk file

How To
#1

How to restart calculation using .fchk file that is generated by using keyword IQMOL_FCHK true.
?

#2

You cannot restart calculations using an FCHK file. FCHK file includes certain output data that can be read and visualized by IQmol for example. Please refer to the Q-Chem Manual for elaborate discussion on FCHK files.

Further, not all types of calculations can be restarted with Q-Chem. What type of calculation do you want to restart? Please report a sample input using the preformatted text option (</>).

#3

You can restart a Q-Chem calculation using a .fch/.fchk/.FChk file, via using the fch2qchem utility of MOKIT. Assuming we have a file O2_uhf.FChk, which includes the open-shell singlet UHF wave function information, we firstly standardize this file by running the following Python script

from mokit.lib.qchem import standardize_fch
standardize_fch('O2_uhf.FChk')

A new file O2_uhf_std.fch would be generated. Then we run the following Shell command

fch2qchem O2_uhf_std.fch

The Q-Chem input file O2_uhf_std.in would be generated. Cartesian coordinates, basis set data and UHF keywords are already written in this file. And the wave function data is automatically put into Q-Chem scratch directory $QCSCRATCH/. You can modify the input file as you wish, if we simply submit the Q-Chem job, e.g.

qchem -nt 2 -np 1 O2_uhf_std.in O2_uhf_std.out O2_uhf_std

It would be accomplished immediately since UHF converged orbitals are used. Related output is

 -------------------------------------------------------
 ---------------------------------------
  Cycle       Energy         DIIS Error
 ---------------------------------------
    1    -149.6041432637      2.49E-09
    2    -149.6041432384      2.47E-10 Convergence criterion met
 ---------------------------------------
 <S^2> = 1.0173

Hope this will do some help.