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The molar spin susceptibilities $\chi(T)$ of Na-TCNQ, K-TCNQ and Rb-TCNQ(II)are fit quantitatively to 450 K in terms of half-filled bands of threeone-dimensional Hubbard models with extended interactions using exact resultsfor finite systems. All three models have bond order wave (BOW) and chargedensity wave (CDW) phases with boundary $V = V_c(U)$ for nearest-neighborinteraction $V$ and on-site repulsion $U$. At high $T$, all three salts haveregular stacks of $\rm TCNQ^-$ anion radicals. The $\chi(T)$ fits place Na andK in the CDW phase and Rb(II) in the BOW phase with $V \approx V_c$. The Na andK salts have dimerized stacks at $T < T_d$ while Rb(II) has regular stacks at100K. The $\chi(T)$ analysis extends to dimerized stacks and to dimerizationfluctuations in Rb(II). The three models yield consistent values of $U$, $V$and transfer integrals $t$ for closely related $\rm TCNQ^-$ stacks. Modelparameters based on $\chi(T)$ are smaller than those from optical data that inturn are considerably reduced by electronic polarization from quantum chemicalcalculation of $U$, $V$ and $t$ on adjacent $\rm TCNQ^-$ ions. The $\chi(T)$analysis shows that fully relaxed states have reduced model parameters comparedto optical or vibration spectra of dimerized or regular $\rm TCNQ^-$ stacks.

Magnetic susceptibility of alkali-TCNQ salts and extended Hubbard models with bond order and charge density wave phases