Equation sheet#

Units#

Constants#

Energy Constant

Value

h=6.631034[Js]

mu=1.661027[kg]

kB=1.381023[JK1]

NA=6.021023[mol1]

c=3.0108[ms1]

me=9.10938370151031[kg]

RH=109680[cm1]

e=1.6021766341019[C]

Energy Unit Converter#

  • See here for an interactive option.

Unit

J

eV

cm1

hartree

Hz

J

1

6.241811018

5.034451022

2.2941017

1.509301033

eV

1.602101019

1

8065.73

0.0367502

2.418041014

cm1

1.986301023

1.23981104

1

4.55633106

2.997931010

hartree

43.601019

27.2107

219474.63

1

6.579661015

Hz

6.625611034

4.135581015

3.335651011

1.519831016

1

From classical to Quantum#

Blackbody radiation#

Description

Equations

Energy quantization

E=nhν

Average energy of an oscillating dipole

Eosc=hνehν/kBT1

Spectral radiation density of blackbody (Planck)

ρ(ν,T) dν=8πhν3c31ehν/kBT1 dν

Spectral radiation density of blackbody (classical)

ρ(ν,T) dν=8πhν3c3kBTdν

Wave-particle duality#

Description

Equations

Energy of light

E=hν

Photoelectric effect
Kinetic energy of ejected photoelectron

Ek=hνΦ

de Broglie relation

p=hλ

Kinetic energy

Ek=12mv2=p22m

Atomic spectra of hydrogen and Bohr’s model#

Description

Equations

Hydrogen emission lines
n2>n1

ν~=1λ=RH(1n121n22)

Bohr’s radius

r=4πε02mee2

Energy level in Bohr’s model

En=mee48ε02h2n2

Emission of hydrogen atom
n2>n1

ν=mee48ε02h3(1n121n22)

Waves#

Description

Equations

Classical nondispersive wave equation

Ψ(x,t)x2=1v2Ψ(x,t)t2

Wave number

k=2πλ

Frequency

ν=1T

Angular frequency

ω=2πT=2πν

Wave speed

v=λν

Euler’s formula

eiθ=cosθ+isinθ

Solution of wave equation

Ψ(x,t)=Asin(kxωt+ϕ) =Re(Aei(kxωt+ϕ))

Interfering traveling waves give standing wave

Ψ(x,t)=A[sin(kxωt)+sin(kx+ωt)] =2Asin(kx)cos(ωt) =ψ(x)cos(ωt)

Time-independent Schrodinger equation

22md2ψ(x)dx2+V(x)ψ(x)=Eψ(x)

Time-dependent Schrodinger equation

22m2Ψ(x,t)x2+V(x,t)Ψ(x,t)=iΨ(x,t)

Stationary states are standing waves

Ψ(x,t)=ψ(x)ei(E/)t

Normalization

f(x)=Dff dx=1

Orthogonality

Dfg dx=0

Use quantum mechanics when …

1. λparticleLproblem
2. ΔEkbT (discrete energy spectrum)

Quantum-Mechanical Postulates#

  1. The state of a quantum-mechanical particle is completely specified by a wave function Ψ(x,t). The probability that the particle will be found at time t0 in a spatial interval of width dx centered at x0 is given by Ψ(x0,t0)Ψ(x0,t0)dx

  2. For every measurable property of a system, there exists a corresponding operator.

  3. In any single measurement of the observable that corresponds to the operator A^, the only values that will ever be measured are the eigenvalues of that operator.

  4. If the system is in a state described by the wave function Ψ(x,t), and the value of the observatle a is measured once on each of many identically prepared systems, the average value (expectation value) of all of the measurements is given by $a=ΨA^Ψ dxΨΨ dx$

  5. The evolution in time of a quantum-mechanical system is governed by the time-dependent Schrödinger equation $H^Ψ(x,t)=iΨ(x,t)t$

Operators#

Description

1D

3D

Position

x^=x

x^=x

Linear momentum

p^x=iddx

p^=i

Kinetic energy

T^=p^x22m=22md2dx2

T^=22m2

Potential energy

V^=V(x)

V^=V(x)

Total energy Hamiltonian

H^=T^+V^=22md2dx2+V(x)

H^=22m2+V(x)

Simple Quantum Systems#

Stationary states#

Description

Equations

Time dependent Schrodinger equation

H^Ψ(x,t)=iΨ(x,t)t

Time independent Schrodinger equation

H^ψn(x)=Enψn(x)

Stationary state wave function

Ψ(x,t)=ψ(x)T(t)

Time component of wave function

T(t)=eiEt/

Probability of finding particle in an interval

Prob(x,x+dx)=|Ψ(x,t)|2dx=|ψ(x)|2dx

General solution as linear combination of stationary states

ψ(x)=ncnϕn(x)

Expansion coefficients

cn=ϕn|ψ=ϕnψ dx

Normalization

ncn=1

Particle in a 1D box#

Description

Equations

Time independent Schrodinger equation

[22md2dx2+V(x)]ψ(x)=Eψ(x)

Wave function
n=0,1,2,...

ψn(x)=2Lsin(nπxL)

Energy eigenvalues

En=h28mL2n2=2π22mL2n2

Particle in a 3D box#

Description

Equations

Time independent Schrodinger equation

[22m2+V(x)]ψ(x)=Eψ(x)

Wave function
nx=0,1,2,...
ny=0,1,2,...
nz=0,1,2,...

ψnx,ny,nz(x) =ψnx(x)ψny(y)ψnz(z) =2Lx2Ly2Lzsin(nxπxLx)sin(nyπyLy)sin(nzπzLz)

Energy eigenvalues

En=h28m(nx2Lx2+ny2Ly2+nz2Lz2)

Finite potential well#

Description

Equations

Potential

V(x)={0x[0,L] V0elsewhere

Reflection probability

R=(EEV0)2(E+EV0)2

Transmission probability

T=4E(EV0)(EEV0)2

Commutators and Uncertainty#

Description

Equations

Commutator

[A,B]=ABBA

Condition of commutation

[A,B]=0

Standard deviation (uncertainty)

σA=(AA2) =A2A2

Heisenberg uncertainty principle (general)

σAσB12|[A^,B^]|

Heisenberg uncertainty principle (position-momentum)

σxσp2

Spectroscopy#

Vibration: quantum harmonic oscillator#

Description

Equations

Vibrational Schrodinger equation

[22μ1r2r(r2r)+V(r)]ψ(x)=Eψ(x)

Wave function

ψ(x)=R(r)Y(θ,ϕ)

Harmonic approximation

V(r)12kr2

Spring constant

k=μω02

Vibrational Schrodinger equation

[22μ1r2r(r2r)+12kr2]ψ(r)=Eψ(r)

Wave function
n=0,1,2,...

ψ(r)=122n!(απ)1/4Hn(αr)eαr2/2

Hermite polynomials

Hn(r)=()nex2(dndxn)ex2

Constant

α=mω0

Energy eigenvalue
n=0,1,2,...

En=(n+12)ω0

Transition dipole moment

μfi=dμ(x0)dxψf|x^|ψi

Vibrational selection rule

Δn=±1

Rotation: quantum rigid rotor#

Classical rigid rotor#

Description

Equations

Angular momentum

L=x×p=Iω

Linear velocity

v=R0ω

Moment of inertia

I=mR02

Rotational kinetic energy

E=12Iω2=L22I

Quantum rigid rotor#

Description

Equations

Angular momentum operator

L^=x^×p^

z-component of angular momentum operator

Lx=iϕ

Magnitude of angular momentum operator

L^2=L2=2[1sinθθ(sinθθ+1sin2θ2ϕ2)]

Components of L^ does not commute

[L^i,L^j]=iL^k

Components of L^ commute with its magnitude

[L^i,L2]=0

Description

Equations

Rotational Schrodinger equation

22μR02[1r2sinθθ(sinθθ)+1r2sin2θ2ϕ2]Y(θ,ϕ)=EY(θ,ϕ)

Spherical harmonics

Ylm(θ,ϕ)=()m(2l+1)4π(lm)!(l+m)!Plm(cosθ)eimϕ

Legendre polynomial

Plm(x)=12ll!(1x2)m/2d(l+m)dx(l+m)(x21)l

Energy eigenvalues
l=0,1,2,...

El=22Il(l+1)

Angular momentum eigenvalues
l=0,1,2,...

L2Y=2l(l+1)Y

z-component eigenvalues
m=l,...,0,...,l

LzY=mY

Transition dipole moment

μfi=ψf|μzcosθ|ψi

Rotational selection rule

Δl=±1,Δm=0

Hydrogen atom#

Description

Equations

Hydrogen atom Schrodinger equation

[2me1r2r(r2r)+L2mer2e2r]ψ(x)=Eψ(x)

Effective potential

Veff=l(l+1)2mr2e2r

Wave function
n=1,2,...

ψnlm(x)=Rnl(r)Ylm(θ,ϕ)

Energy eigenvalues
n=1,2,...

En=e22a01n2=me4221n2RHn2

Rydberg’s constant

RH=2.179×1018J=13.6 eV

Bohr’s radius

a0=2me2

Radial probability distribution

Pnl(r)dr=r2Rnl2(r)dr

Many Electron and Proton System#

Many electron atom#

Description

Equations

Helium Schrodinger equation

[22m12_KE of e122m22\^KE of e22e2|x1|_e1-N attraction2e2|x2|\^e2-N attraction+e2|x1x2|_e1-e2repulsion]ψ(x1,x2)=Eψ(x1,x2)

Orbital approximation

ψ(x1,x2,,xn)=ϕ(x1)ϕ(x2)ϕ(xn)

Hartree orbital equations

[2i22mZe2|x|+j=1,jiNe2ϕj(x)ϕj(x)|xx|d3x]ϕi(x)=εiiϕi(x)

Spin#

Description

Equations

Components of S^ does not commute

[S^i,S^j]=iS^k

Components of S^ commute with its magnitude

[S^i,S2]=0

Eigenvalue of S^2

S^22s(s+1)

Eigenvalue of S^z

S^zms

Electron spin#

Description

Equations

Electron spin

s=12

Spin up function

α(ms)={1ms=+12 0ms=12

Spin down function

β(ms)={0ms=+12 1ms=12

α is eigenfunction of Sz^

Sz^α=+12α

β is eigenfunction of Sz^

Sz^β=12β

α,β are eigenfunctions of S2^

S2^α=2s(s+1)α=342αS2^β=2s(s+1)β=342β

Normalization

msαα=msββ=1

Orthogonality

msαβ=msβα=0

Identical particles#

Description

Equations

Spin-spin permutation operator

Pijψ(r1,r2,,ri,,rj,,rN)=ψ(r1,r2,,rj,,ri,,rN)

Doing nothing

PijPij=1

Symmetric eigenvalue

λ=1

Anti-symmetric eigenvalue

λ=1

Fermions (e.g. electron)

12-integer spin, anti-symmetric

Bosons

integer spin, symmetric

Pauli exclusion principle

ψ(r1,r2,,ri,,ri,,rN)=ψ(r1,r2,,ri,,ri,,rN)=0

Slater determinant

Ψ(x1,x2,,xN)=1N!|χ1(x1)χ2(x1)χN(x1) χ1(x2)χ2(x2)χN(x2)  χ1(xN)χ2(xN)χN(xN)|

Hartree-Fock orbital equations

[222mZe2|x|]ϕi(r)+j=1N[ϕi(r)e2ϕj(r)ϕj(r)|xx|d3rϕj(r)e2ϕj(r)ϕi(r)|xx|d3r]=εiϕi(r)

Molecular orbital by linear combination of atomic orbitals (MO-LCAO)

ψ(x)=c1ϕ1(x)+c2ϕ2(x)MO=c1(AO)+c2(AO)

Variational principle

E=ψ|H|ψψ|ψ