Subroutine RELAX_BOND

Exponentially decay a bond length towards a final value.

• data(1) = initial bond length
• data(2) = final bond length
• data(3) = initial time
• data(4) = relaxation time

Constraint function is $C = \vert\mathbf{r}_1 - \mathbf{r}_2\vert^2 - d^2$, where

$$d = d_{final} + (d_{init} - d_{final})\exp\left(-\frac{t-t_{init}}{t_{relax}}\right)$$

pos, velo, data -- real(dp), dimension(:), intent(in)

t -- real(dp), intent(in)

C -- real(dp), intent(out)

dC_dr -- real(dp), dimension(size(pos)), intent(out)

dC_dt -- real(dp), intent(out)

CUBIC_BOND subroutine