-- Sofar we calculated eigenstates and expectation values (or spectra) of these -- eigenstates. At 0 K one would measure the expectation value of the lowest eigenstate -- at finite temperature one would measure an average over several states weighted by -- Boltzmann statistics. In this example we calculate the temperature dependent -- x-ray absorption spectra of NiO. (Ni L23 edge 2p to 3d) -- we set the verbosity to 0 in order to minimize the output Verbosity(0) -- the beginning of this file is the same as example 21 where x-ray absorption is calculated -- In order to do crystal-field theory for NiO we need to define a Ni d-shell. -- A d-shell has 10 elements and we label again the even spin-orbitals to be spin down -- and the odd spin-orbitals to be spin up. In order to calculate 2p to 3d excitations we -- also need a Ni 2p shell. We thus have a total of 10+6=16 fermions, 6 Ni-2p and 10 Ni-3d -- spin-orbitals NF=16 NB=0 IndexDn_2p={0,2,4} IndexUp_2p={1,3,5} IndexDn_3d={6,8,10,12,14} IndexUp_3d={7,9,11,13,15} -- just like in the previous example we define several operators acting on the Ni -3d shell OppSx =NewOperator("Sx" ,NF, IndexUp_3d, IndexDn_3d) OppSy =NewOperator("Sy" ,NF, IndexUp_3d, IndexDn_3d) OppSz =NewOperator("Sz" ,NF, IndexUp_3d, IndexDn_3d) OppSsqr =NewOperator("Ssqr" ,NF, IndexUp_3d, IndexDn_3d) OppSplus=NewOperator("Splus",NF, IndexUp_3d, IndexDn_3d) OppSmin =NewOperator("Smin" ,NF, IndexUp_3d, IndexDn_3d) OppLx =NewOperator("Lx" ,NF, IndexUp_3d, IndexDn_3d) OppLy =NewOperator("Ly" ,NF, IndexUp_3d, IndexDn_3d) OppLz =NewOperator("Lz" ,NF, IndexUp_3d, IndexDn_3d) OppLsqr =NewOperator("Lsqr" ,NF, IndexUp_3d, IndexDn_3d) OppLplus=NewOperator("Lplus",NF, IndexUp_3d, IndexDn_3d) OppLmin =NewOperator("Lmin" ,NF, IndexUp_3d, IndexDn_3d) OppJx =NewOperator("Jx" ,NF, IndexUp_3d, IndexDn_3d) OppJy =NewOperator("Jy" ,NF, IndexUp_3d, IndexDn_3d) OppJz =NewOperator("Jz" ,NF, IndexUp_3d, IndexDn_3d) OppJsqr =NewOperator("Jsqr" ,NF, IndexUp_3d, IndexDn_3d) OppJplus=NewOperator("Jplus",NF, IndexUp_3d, IndexDn_3d) OppJmin =NewOperator("Jmin" ,NF, IndexUp_3d, IndexDn_3d) Oppldots=NewOperator("ldots",NF, IndexUp_3d, IndexDn_3d) -- as in the previous example we define the Coulomb interaction OppF0 =NewOperator("U", NF, IndexUp_3d, IndexDn_3d, {1,0,0}) OppF2 =NewOperator("U", NF, IndexUp_3d, IndexDn_3d, {0,1,0}) OppF4 =NewOperator("U", NF, IndexUp_3d, IndexDn_3d, {0,0,1}) -- as in the previous example we define the crystal-field operator Akm = PotentialExpandedOnClm("Oh",2,{0.6,-0.4}) OpptenDq = NewOperator("CF", NF, IndexUp_3d, IndexDn_3d, Akm) -- and as in the previous example we define operators that count the number of eg and t2g -- electrons Akm = PotentialExpandedOnClm("Oh",2,{1,0}) OppNeg = NewOperator("CF", NF, IndexUp_3d, IndexDn_3d, Akm) Akm = PotentialExpandedOnClm("Oh",2,{0,1}) OppNt2g = NewOperator("CF", NF, IndexUp_3d, IndexDn_3d, Akm) -- new for core level spectroscopy are operators that define the interaction acting on the -- Ni-2p shell. There is actually only one of these interactions, which is the Ni-2p -- spin-orbit interaction Oppcldots= NewOperator("ldots", NF, IndexUp_2p, IndexDn_2p) -- we also need to define the Coulomb interaction between the Ni 2p- and Ni 3d-shell -- Again the interaction (e^2/(|r_i-r_j|)) is expanded on spherical harmonics. For the interaction -- between two shells we need to consider two cases. For the direct interaction a 2p electron -- scatters of a 3d electron into a 2p and 3d electron. The radial integrals involve -- the square of a 2p radial wave function at coordinate 1 and the square of a 3d radial -- wave function at coordinate 2. The transfer of angular momentum can either be 0 or 2. -- These processes are called direct and the resulting Slater integrals are F[0] and F[2]. -- The second proces involves a 2p electron scattering of a 3d electron into the 3d shell -- and at the same time the 3d electron scattering into a 2p shell. These exchange processes -- involve radial integrals over the product of a 2p and 3d radial wave function. The transfer -- of angular momentum in this case can be 1 or 3 and the Slater integrals are called G1 and G3. -- In Quanty you can enter these processes by labeling 4 indices for the orbitals, once -- the 2p shell with spin up, 2p shell with spin down, 3d shell with spin up and 3d shell with -- spin down. Followed by the direct Slater integrals (F0 and F2) and the exchange Slater -- integrals (G1 and G3) -- Here we define the operators separately and later sum them with appropriate prefactors OppUpdF0 = NewOperator("U", NF, IndexUp_2p, IndexDn_2p, IndexUp_3d, IndexDn_3d, {1,0}, {0,0}) OppUpdF2 = NewOperator("U", NF, IndexUp_2p, IndexDn_2p, IndexUp_3d, IndexDn_3d, {0,1}, {0,0}) OppUpdG1 = NewOperator("U", NF, IndexUp_2p, IndexDn_2p, IndexUp_3d, IndexDn_3d, {0,0}, {1,0}) OppUpdG3 = NewOperator("U", NF, IndexUp_2p, IndexDn_2p, IndexUp_3d, IndexDn_3d, {0,0}, {0,1}) -- next we define the dipole operator. The dipole operator is given as epsilon.r -- with epsilon the polarization vector of the light and r the unit position vector -- We can expand the position vector on (renormalized) spherical harmonics and use -- the crystal-field operator to create the dipole operator. -- x polarized light is defined as x = Cos[phi]Sin[theta] = sqrt(1/2) ( C_1^{(-1)} - C_1^{(1)}) Akm = {{1,-1,sqrt(1/2)},{1, 1,-sqrt(1/2)}} TXASx = NewOperator("CF", NF, IndexUp_3d, IndexDn_3d, IndexUp_2p, IndexDn_2p, Akm) -- x polarized light is defined as y = Sin[phi]Sin[theta] = sqrt(1/2) I ( C_1^{(-1)} + C_1^{(1)}) Akm = {{1,-1,sqrt(1/2)*I},{1, 1,sqrt(1/2)*I}} TXASy = NewOperator("CF", NF, IndexUp_3d, IndexDn_3d, IndexUp_2p, IndexDn_2p, Akm) -- z polarized light is defined as z = Cos[theta] = C_1^{(0)} Akm = {{1,0,1}} TXASz = NewOperator("CF", NF, IndexUp_3d, IndexDn_3d, IndexUp_2p, IndexDn_2p, Akm) -- besides linear polarized light one can define circular polarized light as the sum of -- x and y polarizations with complex prefactors TXASr = sqrt(1/2)*(TXASx - I * TXASy) TXASl =-sqrt(1/2)*(TXASx + I * TXASy) -- once all operators are defined we can set some parameter values. -- the value of U drops out of a crystal-field calculation as the total number of electrons -- is always the same U = 0.000 -- F2 and F4 are often referred to in the literature as J_{Hund}. They represent the energy -- differences between different multiplets. Numerical values can be found in the back of -- my PhD. thesis for example. http://arxiv.org/abs/cond-mat/0505214 F2dd = 11.142 F4dd = 6.874 -- F0 is not the same as U, although they are related. Unimportant in crystal-field theory -- the difference between U and F0 is so important that I do include it here. (U=0 so F0 is not) F0dd = U+(F2dd+F4dd)*2/63 -- in crystal field theory U drops out of the equation, also true for the interaction between the -- Ni 2p and Ni 3d electrons Upd = 0.000 -- The Slater integrals between the 2p and 3d shell, again the numerical values can be found -- in the back of my PhD. thesis. (http://arxiv.org/abs/cond-mat/0505214) F2pd = 6.667 G1pd = 4.922 G3pd = 2.796 -- F0 is not the same as U, although they are related. Unimportant in crystal-field theory -- the difference between U and F0 is so important that I do include it here. (U=0 so F0 is not) F0pd = Upd + G1pd*1/15 + G3pd*3/70 -- tenDq in NiO is 1.1 eV as can be seen in optics or using IXS to measure d-d excitations tenDq = 1.100 -- the Ni 3d spin-orbit is small but finite zeta_3d = 0.081 -- the Ni 2p spin-orbit is very large and should not be scaled as theory is quite accurate here zeta_2p = 11.498 -- we can add a small magnetic field, just to get nice expectation values. (units in eV... ) -- we define a magnetic field in units of tesla EnergyUnits.Tesla.value is a constant -- expressing Tesla in units of eV B = 10*EnergyUnits.Tesla.value -- once all parameters are set we can define the Hamiltonian for both the ground-state -- and the excited state as a sum of operators multiplied with the numerical interaction strength Hamiltonian = F0dd*OppF0 + F2dd*OppF2 + F4dd*OppF4 + tenDq*OpptenDq + zeta_3d*Oppldots + B*(2*OppSz + OppLz) XASHamiltonian = Hamiltonian + zeta_2p * Oppcldots + F2pd * OppUpdF2 + G1pd * OppUpdG1 + G3pd * OppUpdG3 -- we set restrictions to have 6 electrons in the p-shell and 8 electrons in the d-shell StartRestrictions = {NF, NB, {"111111 0000000000",6,6}, {"000000 1111111111",8,8}} -- and we calculate all 45 eigenstates Npsi=45 psiList = Eigensystem(Hamiltonian, StartRestrictions, Npsi) -- Boltzmann statistics contains the exponent of the eigen energy. In order to prevent -- number overflow we set later the ground-state energy to zero. Here we calculate -- the ground state energy Egrd = psiList[1] * Hamiltonian * psiList[1] -- In order to get some information on these eigenstates it is good to plot expectation values -- We first define a list of all the operators we would like to calculate the expectation value of oppList={Hamiltonian, OppSsqr, OppLsqr, OppJsqr, OppSz, OppLz, Oppldots, OppF2, OppF4, OppNeg, OppNt2g}; -- next we loop over all operators and all states and print the expectation value print(" "); for i = 1,#psiList do for j = 1,#oppList do expectationvalue = Chop(psiList[i]*oppList[j]*psiList[i]) io.write(string.format("%6.3f ",expectationvalue)) end io.write("\n") end -- now we can calculate temperature averaged expectation values -- The temperature we will take here is 10 Kelvin (again we enter it in units of eV) T = 10 * EnergyUnits.Kelvin.value -- we will calculate the partition function Z Z=0 -- the total magnetic moment M M=0 -- the total spin moment MS MS=0 -- the total angular moment ML ML=0 -- and temperature averaged spectra for z, r and l polarized light. Spectra_z=0 Spectra_r=0 Spectra_l=0 -- the temperature averaged spectra are calculated as sums over the different states -- weighted by the Boltzmann occupation. In order to make these sums we set them first to -- zero (done above) -- and now we can make the sums for j=1, 3 do Z = Z + exp(-(psiList[j] * Hamiltonian * psiList[j] - Egrd)/T) M = M + psiList[j] * (2 * OppSz + OppLz) * psiList[j] * exp(-(psiList[j] * Hamiltonian * psiList[j] - Egrd)/T) MS = MS + psiList[j] * (OppSz) * psiList[j] * exp(-(psiList[j] * Hamiltonian * psiList[j] - Egrd)/T) ML = ML + psiList[j] * (OppLz) * psiList[j] * exp(-(psiList[j] * Hamiltonian * psiList[j] - Egrd)/T) Spectra_z = Spectra_z + CreateSpectra(XASHamiltonian, TXASz,psiList[j], {{"Emin",-10}, {"Emax",20}, {"NE",3500}, {"Gamma",1.0}}) * exp(-(psiList[j] * Hamiltonian * psiList[j] - Egrd)/T) Spectra_r = Spectra_r + CreateSpectra(XASHamiltonian, TXASr,psiList[j], {{"Emin",-10}, {"Emax",20}, {"NE",3500}, {"Gamma",1.0}}) * exp(-(psiList[j] * Hamiltonian * psiList[j] - Egrd)/T) Spectra_l = Spectra_l + CreateSpectra(XASHamiltonian, TXASl,psiList[j], {{"Emin",-10}, {"Emax",20}, {"NE",3500}, {"Gamma",1.0}}) * exp(-(psiList[j] * Hamiltonian * psiList[j] - Egrd)/T) end -- In order to normalize we should device by the partition function Z M = M / Z MS = MS / Z ML = ML / Z Spectra_z = Spectra_z/Z Spectra_r = Spectra_r/Z Spectra_l = Spectra_l/Z -- and we can print the results to the screen print("For a magnetic field of ",B/EnergyUnits.Tesla.value,"Tesla") print("At temperature ",T/EnergyUnits.Kelvin.value," Kelvin the magnetic moment is",M) print("The spin contribution is",MS) print("The angular contribution is",ML) -- we can calculate the isotropic spectra and the magnetic circular dichroism Spectra_iso = (Spectra_z + Spectra_l + Spectra_r)/3 Spectra_XMCD = (Spectra_r - Spectra_l) -- and print them to file Spectra_iso.Print({{"file", "TemperatureXASSpecIso.dat"}}); Spectra_XMCD.Print({{"file", "TemperatureXASSpecXMCD.dat"}}); -- from here on you can use your favorite program to plot these spectra -- I include a gnuplot script to make these plots -- a gnuplot script to make the plots gnuplotInput = [[ set autoscale set xtic auto set ytic auto set style line 1 lt 1 lw 1 lc rgb "#FF0000" set style line 2 lt 1 lw 1 lc rgb "#0000FF" set xlabel "E (eV)" font "Times,12" set ylabel "Intensity (arb. units)" font "Times,12" set out 'Temperature.ps' set size 1.0, 1.0 set terminal postscript portrait enhanced color "Times" 8 plot "TemperatureXASSpecIso.dat" u 1:(-\$3) title 'Iso ' with lines ls 1,\ "TemperatureXASSpecXMCD.dat" u 1:(-\$3) title 'XMCD' with lines ls 2 ]] -- write the gnuplot script to a file file = io.open("Temperature.gnuplot", "w") file:write(gnuplotInput) file:close() -- call gnuplot to execute the script os.execute("gnuplot Temperature.gnuplot ") -- change the postscript file to pdf or eps os.execute("ps2pdf Temperature.ps ; ps2eps Temperature.ps ; mv Temperature.eps temp.eps ; eps2eps temp.eps Temperature.eps ; rm temp.eps")