An effective way of assuring the reliability of implementation
of many functionalities is to compare analytic and numerical forces.
If any program bug is introduced, they will not be consistent with each
other. To do this, one can run an automatic tester by

**For serial running**

% ./openmx -forcetest 0

% ./openmx -forcetest 0 "mpirun -np 4 openmx"where '0' is a flag to specify energy terms to be included in the consistency check, and one can change 0 to 8. Each number corresponds to

flag 0 1 2 3 4 5 6 7 8 Kinetic 1 0 1 0 0 0 0 0 0 Non-local 1 0 0 1 0 0 0 0 0 Neutral atom 1 0 0 0 1 0 0 0 0 diff Hartree 1 0 0 0 0 1 0 0 0 Ex-Corr 1 0 0 0 0 0 1 0 0 E. Field 1 0 0 0 0 0 0 1 0 Hubbard U 1 0 0 0 0 0 0 0 1

where '1' means that it is included in the force consistency check. In a directory 'work/force_example', there are 36 test inputs which are used for the force consistency check. After finishing the test, a file 'forcetest.result' is generated in the directory 'work'. You will see results of the comparison as follows:

force_example/C2_GGA.dat flag= 0 Numerical force= -(Utot(s+ds)-Utot(s-ds))/(2*ds) ds= 0.0003000000 Forces (Hartree/Bohr) on atom 1 x y z Analytic force -1.676203071292 -1.397113794193 -1.117456296887 Numerical force -1.676101156844 -1.397036485449 -1.117288361652 diff -0.000101914447 -0.000077308744 -0.000167935235 force_example/C2_LDA.dat flag= 0 Numerical force= -(Utot(s+ds)-Utot(s-ds))/(2*ds) ...... ....

t-ozaki 2013-05-22