c---------------------------------------------------------------------
      subroutine tnp1_step2
c  Step 2 of the velocity Verlet algorithm: update velocities
      implicit real*8 (a-h,o-z)
      include 'DIMENSIONS'
      include 'COMMON.CONTROL'
      include 'COMMON.VAR'
      include 'COMMON.MD'
      include 'COMMON.CHAIN'
      include 'COMMON.DERIV'
      include 'COMMON.GEO'
      include 'COMMON.LOCAL'
      include 'COMMON.INTERACT'
      include 'COMMON.IOUNITS'
      include 'COMMON.NAMES'

      double precision d_time_s12

      do i=0,2*nres
       do j=1,3
        d_t(j,i)=d_t_new(j,i)
       enddo
      enddo

      call kinetic(EK)
      EK=EK/s12_np**2

      d_time_s12=0.5d0*s12_np*d_time

      do j=1,3
        d_t(j,0)=d_t_new(j,0)+d_a(j,0)*d_time_s12
      enddo
      do i=nnt,nct-1
        do j=1,3
          d_t(j,i)=d_t_new(j,i)+d_a(j,i)*d_time_s12
        enddo
      enddo
      do i=nnt,nct
        if (itype(i).ne.10) then
          inres=i+nres
          do j=1,3
            d_t(j,inres)=d_t_new(j,inres)+d_a(j,inres)*d_time_s12
          enddo
        endif
      enddo 

cd      write(iout,*) 'pistar',pistar,EK,E_old,potE,s12_np
      pistar=pistar+(EK-0.5*(E_old+potE)
     &       -dimen*Rb*t_bath*log(s12_np)+H0-dimen*Rb*t_bath)*d_time
      tmp=1+pistar/(2*Q_np)*0.5*d_time
      s_np=s12_np*tmp**2
      pi_np=pistar/tmp

      return
      end