有做自由能方向的大佬吗 能否讲解一下例子

variable TK equal 300.0
variable PBAR equal 1.0
fix SHAKE all shake 0.0001 20 0 b 2 a 2
neighbor 2.0 bin
timestep 1.0
velocity all create ${TK} 12345
thermo_style multi
thermo 5000
fix TPSTAT all npt temp ${TK} ${TK} 100 iso ${PBAR} ${PBAR} 1000
set type 1*2 charge 0.0
run 100000
reset_timestep 0
variable lambda equal ramp(0.0,1.0)
variable q1 equal -0.24*v_lambda
variable q2 equal 0.06*v_lambda
fix ADAPT all adapt/fep 100000 &
pair lj/cut/tip4p/long/soft lambda 1*2 3*4 v_lambda &
atom charge 1 v_q1 &
atom charge 2 v_q2 &
after yes
fix PRINT all print 100000 "adapt lambda = ${lambda} q1 = ${q1} q2 = ${q2}"
variable dlambda equal 0.002
variable dq1 equal -0.24*v_dlambda
variable dq2 equal 0.06*v_dlambda
compute FEP all fep ${TK} &
pair lj/cut/tip4p/long/soft lambda 1*2 3*4 v_dlambda &
atom charge 1 v_dq1 &
atom charge 2 v_dq2
fix FEP all ave/time 20 4000 100000 c_FEP[1] c_FEP[2] file fdti01.lmp
dump TRAJ all custom 20000 dump.lammpstrj id mol type element x y z ix iy iz
dump_modify TRAJ element C H O H
run 2000000