112 lines
3.5 KiB
C++
112 lines
3.5 KiB
C++
/**********************************************************
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This software is part of J.-S. Caux's ABACUS library.
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Copyright (c) J.-S. Caux.
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-----------------------------------------------------------
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File: XXZ_gpd_StagSz_h0.cc
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Purpose: Compute the staggered magentization of XXZ_gpd in zero field.
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***********************************************************/
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#include "ABACUS.h"
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using namespace std;
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using namespace ABACUS;
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int main( int argc, char* argv[])
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{
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if (!(argc == 3 || argc == 5)) { // provide some info
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cout << endl << "This code computes the (1/N) (-1)^j S^z_j on-site staggered magnetization for XXZ_gpd in zero field." << endl;
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cout << "First option: provide two arguments: anisotropy Delta (> 1) and system size N (even)." << endl;
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cout << "Second option: provide five arguments: system size N (even), Delta min, Delta max, NDelta." << endl;
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cout << "The output is Delta, N, stag mag, energy gap." << endl;
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ABACUSerror("");
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}
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else if (argc == 3) {
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DP Delta = atof(argv[1]);
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if (Delta <= 1.0) ABACUSerror("Provide Delta > 1.");
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int N = atoi(argv[2]);
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if (N % 2) ABACUSerror("Provide an even Delta.");
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int M = N/2;
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// Define the chain: J, Delta, h, Nsites
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Heis_Chain chain(1.0, Delta, 0.0, N);
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Heis_Base gbase(chain, M);
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XXZ_gpd_Bethe_State gstate(chain, gbase);
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gstate.Compute_All(true);
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XXZ_gpd_Bethe_State estate(chain, gbase);
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estate.Ix2[0][0] = M+1; // umklapp excitation
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estate.Compute_All(true);
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stringstream basestrstream;
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basestrstream << M-2 << "x1";
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string basestr = basestrstream.str();
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Heis_Base basegap(chain, basestr);
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XXZ_gpd_Bethe_State estategap(chain, basegap);
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estategap.Compute_All(true);
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if (!gstate.conv) ABACUSerror("Ground state did not converge.");
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if (!estate.conv) ABACUSerror("Umklapp state did not converge.");
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if (!estategap.conv) ABACUSerror("Gap state did not converge.");
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cout << Delta << "\t" << N << "\t" << setprecision(12) << exp(real(ln_Sz_ME (gstate, estate)))/sqrt(N) << "\t" << estategap.E - gstate.E << endl;
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}
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else if (argc == 5) { // Do a scan in Delta
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int N = atoi(argv[1]);
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if (N % 2) ABACUSerror("Provide an even Delta.");
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int M = N/2;
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DP Deltamin = atof(argv[2]);
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if (Deltamin <= 1.0) ABACUSerror("Provide Deltamin > 1.");
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DP Deltamax = atof(argv[3]);
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if (Deltamin <= 1.0) ABACUSerror("Provide Deltamax > Deltamin.");
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int NDelta = atoi(argv[4]);
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for (int iDelta = 0; iDelta <= NDelta; ++iDelta) {
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DP Delta = (Deltamin * (NDelta -iDelta) + Deltamax * iDelta)/NDelta;
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// Define the chain: J, Delta, h, Nsites
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Heis_Chain chain(1.0, Delta, 0.0, N);
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Heis_Base gbase(chain, M);
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XXZ_gpd_Bethe_State gstate(chain, gbase);
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gstate.Compute_All(true);
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XXZ_gpd_Bethe_State estate(chain, gbase);
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estate.Ix2[0][0] = M+1; // umklapp excitation
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estate.Compute_All(true);
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stringstream basestrstream;
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basestrstream << M-2 << "x1";
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string basestr = basestrstream.str();
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Heis_Base basegap(chain, basestr);
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XXZ_gpd_Bethe_State estategap(chain, basegap);
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estategap.Compute_All(true);
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if (!gstate.conv) ABACUSerror("Ground state did not converge.");
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if (!estate.conv) ABACUSerror("Umklapp state did not converge.");
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if (!estategap.conv) ABACUSerror("Gap state did not converge.");
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cout << Delta << "\t" << N << "\t" << setprecision(12) << exp(real(ln_Sz_ME (gstate, estate)))/sqrt(N) << "\t" << estategap.E - gstate.E << endl;
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}
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}
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return(0);
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}
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