- #1
Heath Watts
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Hi,
I'm trying to learn quantum physics (chemistry) on my own so that my work with Gaussian and Q-Chem for electronic structural modeling is less of a black box for me. I've reached the harmonic oscillator point in McQuarrie's Quantum Chemistry book and I'm having trouble justifying a step in his math. It's the integral of force with respect to x.
Integrate[m*(d2x/dt2), dx]
This says integrate the second derivative of time with respect to t for the integration variable x.
Changing the variable of integration to time gives:
Integrate[m*(d2x/dt2)*(dt/dt), dx]
or
Integrate[m*(d2x/dt2)*(dx/dt), dt]
Then something occurs here:
Integrate[m*(d(dx/dt)/dt)*(dx/dt), dt]
Integrate[(m/2)*d((dx/dt)*(dx/dt))/dt, dt]
Integrate[(m/2)*d((dx/dt)^2)/dt, dt]
What calculus rule have I forgotten that says that
(d2x/dt2)*(dx/dt)=(1/2)*d((dx/dt)^2)/dt
I can't seem to find it in any of my old textbooks or online. I hope that my notation is clear. I appreciate your help. If you can direct me to a website that explains this rule, I'd appreciate it.
Thanks,
Heath
I'm trying to learn quantum physics (chemistry) on my own so that my work with Gaussian and Q-Chem for electronic structural modeling is less of a black box for me. I've reached the harmonic oscillator point in McQuarrie's Quantum Chemistry book and I'm having trouble justifying a step in his math. It's the integral of force with respect to x.
Integrate[m*(d2x/dt2), dx]
This says integrate the second derivative of time with respect to t for the integration variable x.
Changing the variable of integration to time gives:
Integrate[m*(d2x/dt2)*(dt/dt), dx]
or
Integrate[m*(d2x/dt2)*(dx/dt), dt]
Then something occurs here:
Integrate[m*(d(dx/dt)/dt)*(dx/dt), dt]
Integrate[(m/2)*d((dx/dt)*(dx/dt))/dt, dt]
Integrate[(m/2)*d((dx/dt)^2)/dt, dt]
What calculus rule have I forgotten that says that
(d2x/dt2)*(dx/dt)=(1/2)*d((dx/dt)^2)/dt
I can't seem to find it in any of my old textbooks or online. I hope that my notation is clear. I appreciate your help. If you can direct me to a website that explains this rule, I'd appreciate it.
Thanks,
Heath