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We succeeded in remarkably nice theoretical description of the temperature dependence of the paramagnetic susceptibility of Ba$_2$YMoO$_6$ in the whole temperature range as originating from the atomic-scale discrete electronic structure of Mo$^{5+}$ ions in the 4d$^1$ configuration resulting from crystal-field and spin-orbit interactions. A strong violation of the Curie-Weiss law and a nonmagnetic state of BYMo experimentally-observed down to 50 mK is caused by the dramatical reduction of the Mo-ion magnetic moment. The quantitative reproduction of $\chi$(T) proves that almost all Mo ions are in the Mo$^{5+}$ state over the whole temperature range.

We have for the first time calculated low-energy electronic structure both in paramagnetic and magnetic state as well as zero-temperature properties and thermodynamics. We consistently described magnetic properties of CoO in agreement with its insulating ground state. The orbital moment of 1.42 mu_B gives 35 contribution to the total moment of 4.04 mu_B at T =0 K. We have calculated from this low-energy electronic structure the temperature dependence of the specific heat being in nice agreement with experimental data. In our approach CoO is an insulator independently on distortions and the magnetic order., Comment: 3 pages, 2 figures embedded

Magnetic properties of stechiometric Cs2AgF4 have been calculated within a very strong correlation limit taking into account a low-symmetry crystal field and the intra-atomic spin-orbit coupling of the Ag2+ ion. We consistently explain the insulating ground state and the magnetic state revealing the spin gap of 2.6 meV below Tc of 14.9 K. A d-d excitation of 2.0-2.3 eV related to the t2g-eg promotion energy (=10Dq) is a reason for the lilac colour of Cs2AgF4. Our approach can be experimentally verified by the measurement of the g factor (gz =2.12 and gy =2.52) and the absorption energy at 2.0-2.3 eV., Comment: 4 pages, 2 figures embedded

We have described properties of LiCoO_2 within the Quantum Atomistic Solid State (QUASST) theory taking into account very strong electron correlations, predominantly of the intra-atomic origin, spin-orbit coupling and the detailed local crystallographic surroundings and its symmetry. Properties of LiCoO_2 are consistently explained together with NaCoO_2 and LaCoO_3 - in all of these compounds the Co^3+ ions occur in the low-spin state. This low-spin state is the effect of the relatively strong crystal-field interactions (B_4^z = +320 K <=> 10Dq = 3.3 eV) and is a manifestation of the very large orbital moment of the Co^3+ ion., Comment: 4 pages, 3 figures embedded

We have calculated from first-principles the octupolar interactions of the Ni2+ ion in NiO, which gives the theoretical basis for the ionic description of properties of NiO with fully localized strongly-correlated eight d electrons. A failure of the up-now first principles ionic calculations for NiO was largely due to too small values taken for the octupolar moment of the transition-metal atom, largely generated by too small value for . Our many-electron crystal-field based approach enables successful calculations of the electronic structure and magnetic properties both in the paramagnetic and in magnetically-ordered state as well as zero-temperature properties and thermodynamics., Comment: 4 pages, 3 figures embedded

In contrary to authors of Phys. Rev. Lett. 93, 126406 (2004) claiming "the band picture to be a reasonable starting point for the description of the electronic structure of NiO, much better than the ligand-field picture", we argue that the many-electron CEF approach is physically adequate starting point for discussion of the electronic structure and magnetism of NiO., Comment: 2 pages

In contrary to customarily consideration of the Jahn-Teller theorem for 3d-ion compounds in the orbital space only we point out that it has to be considered in the spin-orbital space. It is despite the weakness of the intraatomic spin-orbit coupling. A direct motivation for this paper is an erroneous claim of a recent Phys. Rev. Lett. 96 (2006) 027201 paper that the high-spin t2g4eg2 state of the 3d6 configuration is not Jahn-Teller active., Comment: 2 pages, 2 figures embedded

In contrary to a claim of the recent Phys. Rev. Lett. 96 (2006) 027201 paper we maintain that the first excited state in LaCoO3 is the high-spin (HS) state (a lowest quasi-triplet from the octahedral subterm 5T2g of the 5D term, Phys. Rev. B 67 (2003) 172401) in agreement with the Tanabe-Sugano diagram., Comment: 1 page

We have performed calculations of the electronic structure of LaCoO3 from first principles, assuming the atomistic construction of matter and the electrostatic origin of the crystal-field splitting. In our atomic-like approach QUASST the d electrons of the Co3+ ion in LaCoO3 form the highly-correlated atomic-like system 3d6 with the singlet ground state 1A1 (an octahedral subterm from the 1I term) and the excited octahedral subterm 5T2g of the 5D term. In the spin-orbital space, being physically adequate, this high-spin state is Jahn-Teller active. We take the ESR experiment of Noguchi et al., Phys. Rev. B 66, 094404 (2002), as confirmation of the existence of the discrete electronic structure for 3$d$ electron states in LaCoO3 in the meV scale postulated in QUASST., Comment: 4 pages, 1 figure embedded

We claim that for calculations of the electronic structure of 3d oxides very strong electron correlations have to be taken into account similarly to those assumed in many-electron crystal field approach. For Co3+ ions in NaxCoO2.yH2O there are 15 low lying many-electron states within 0.1 eV as can be obtained in the many-electron CEF approach with taking into account the spin-orbit coupling. We claim, that the used by us Hamiltonian for the trigonal distortion is correct., Comment: 4 pages, 3 fig embeded

Magnetic properties of stechiometric YTiO3 has been calculated within the single-ion-based paradigm taking into account the low-symmetry crystal field and the intra-atomic spin-orbit coupling of the Ti3+ ion. Despite of the very simplified approach the calculations reproduce perfectly the value of the magnetic moment and its direction as well as temperature dependence of the magnetic susceptibility chi(T). It turns out that the spin-orbit coupling is fundamentally important for 3d magnetism and magnetic properties are determined by lattice distortions., Comment: 5 pages, 4 Figs embedded

We claim that any approach neglecting the spin-orbit coupling and the orbital magnetism is not physically adequate for 3d oxides, including NiO, and that in reaching "excellent agreement" in a Phys. Rev. Lett. 93, 126406 (2004) paper too small experimental value of 1.9 muB has been taken for the Ni magnetic moment despite publication of a new experimental value of 2.2 muB, at 300 K yielding 2.6 muB at T = 0 K, already in a year of 1998., Comment: 2 pages

We have calculated the electronic structure of V2O3 associated with the V3+ ions taking into account strong on-site electron correlations and the spin-orbit coupling. Closely lying 9 states of the subterm 3T1g are a physical reason for exotic phenomena of V2O3. Electronic structure and magnetism of V3+ ions in the octahedral surroundings are strongly susceptible to lattice distortions and magnetic interactions. Our approach accounts both for the insulating ground state, magnetism, including its orbital contribution, as well as thermodynamical properties., Comment: 2 pages, 2 figures embedded

We have shown the existence of localized crystal-field states in conducting magnetic materials coexisting with conduction electrons in CeAl3, UPd2Al3 and YbRh2Si2. We point out that the magnetism is strongly correlated with the very detailed local atomic-scale crystal structure., Comment: 3 pages, 2 figures embedded

We argue that the electronic structure considered in a Phys. Rev. Lett. paper 94 (2005) 146402 of the Co3+ ion in the CoO6 octahedron of NaxCoO2 is completely wrong. The presented Fig. 1 is redrawn here as Fig. 1. For physically adequate electronic structure it is necessary to take into account strong intra-atomic electron correlations and spin-orbit coupling. For Co3+ ions there are 15 low lying many-electron states within 0.1 eV as can be obtained in the many-electron CEF approach., Comment: 4 pages, with 3 figures embedded, 20 refs

The existence of CEF states and the magnetism in conducting compounds NdAl2, UPd2Al3 and YbRh2Si2 is discussed. We point out that in metallic compounds localized crystal-field states coexist with conduction electrons. These compounds are physical realization of an anisotropic spin liquid, which in case of the atomic-like configuration with an odd number of f electrons, is unstable with respect to spin fluctuations for T->0K. YbRh2Si2 is discussed as a compound with the Kramers doublet ground state with a very low magnetic ordering temperature being a reason for the quantum critical point phenomena at low T., Comment: 4 pages, 3 figures embeded

In this contribution we derive and discuss energy levels of the strongly-correlated d2 configuration of the V3+ ion (LaVO3) and of d4 configuration of the Mn3+ ion (LaMnO3) in the octahedral surroundings in the presence of the spin-orbit coupling and the resulting magnetic properties. We take into account very strong correlations among the d electrons and work with strongly-correlated atomic-like electronic systems, ground term of which is, also in a solid, described by two Hund's rules quantum numbers. In a solid we take into account the influence of crystal-field interactions, predominantly of the cubic (octahedral) symmetry. We describe both paramagnetic state and the magnetically-ordered state getting a value of 1.3 uB for the V3+ -ion magnetic moment in the ordered state at 0 K for LaVO3 (3T1g) and of 3.7 uB for LaMnO3 (5Eg). A remarkably consistent description of both zero-temperature properties and thermodynamic properties indicates on the high physical adequacy of the applied atomic approach. We point out the necessity to unquench the orbital moment in 3d-ion compounds. We claim that the intra-atomic spin-orbit coupling and strong electron correlations are indispensable for the physically adequate description of electronic and magnetic properties of LaVO3 and LaMnO3., Comment: 4 pages, 3 figures embedded

We point out the high physical correctness of the use and the concept of the crystal-field approach, even if is used to metallic magnetic materials of transition-metal 3d/4f/5f compounds. We discuss the place of the crystal-field theory in modern solid-state physics and we point out the necessity to consider the crystal-field approach with the spin-orbit coupling and strong electron correlations, as a contrast to the single-electron version of the crystal field customarily used for 3d electrons. We have extended the strongly-correlated crystal-field theory to a Quantum Atomistic Solid-State Theory (QUASST) to account for the translational symmetry and inter-site spin-dependent interactions indispensable for formation of magnetically-ordered state. We have correlated macroscopic magnetic and electronic properties with the atomic-scale electronic structure for ErNi5, UPd2Al3, FeBr2, LaCoO3 and LaMnO3. In QUASST we have made unification of 3d and rare-earth compounds in description of the low-energy electronic structures and magnetism of open 3d-/4f-/5f-shell electrons. QUASST offers consistent description of zero-temperature properties and thermodynamic properties of 4f-/5f-/3d-atom containing compounds. Our studies indicate that it is the highest time to unquench the orbital magnetism in 3d oxides., Comment: 10 pages, 5 figures embedded

We have calculated magnetic properties and the electronic structure of NiO both in the paramagnetic and in magnetically-ordered state as well as zero-temperature properties and thermodynamics within the strongly-correlated crystal-field approach. It is in agreement with a Mott's suggestion that NiO is an insulator due to strong electron correlations. We have quantified crystal-field, spin-orbit and magnetic interactions of the Ni2+ ion in NiO. We have obtained that E_dd >> E_CF(=2.0 eV) >> E_{s-o}(=0.29 eV) > E_mag(=0.07 eV). The orbital moment of 0.54 mu_B amounts at 0 K, in the magnetically-ordered state, to about 20% of the total moment (2.53 mu_B). Our studies indicate that it is the highest time to "unquench" orbital magnetic moment in 3d solid-state physics and the necessity to take always into account strong intra-atomic correlations among d electrons and the intra-atomic spin-orbit coupling. Pacs: 75.25.+z, 75.10.Dg Keywords: Crystalline Electric Field, 3d oxides, magnetism, spin-orbit coupling NiO, Comment: 4 pages in ReVTeX4, 4 figures

The orbital and spin moment of the Ni2+ ion in NiO has been calculated within the quasi-atomic approach. The orbital moment of 0.46 mu_B amounts at 0 K, in the magnetically-ordered state, to about 20% of the total moment (2.45 mu_B). For this outcome, being in nice agreement with the recent experimental finding of the orbital moment, taking into account the intra-atomic spin-orbit coupling is indispensable. PACS: 75.25.+z, 75.10.Dg Keywords: Crystalline Electric Field, 3d oxides, magnetism, NiO, Comment: 6 pages in RevTeX4, 4 figures

We claim that crystal field (CEF) levels exist in UPd2Al3 in contrary to a recent claim of Hiess et al. (cond-mat/0411041) and Bernhoeft et al. (cond-mat/0411042), that there is no experimental evidence for discrete crystal field levels in this superconducting heavy-fermion antiferromagnet. We claim that excitations revealed by Krimmel et al. (J. Phys.: Condens. Matter 8 (1996) 1677 in inelastic-neutron-scattering (INS) studies are i) crystal-field excitations described by us within ii) the 5f3 (U3+) configuration. Moreover, our 5f3 (U3+) scheme, presented in Physica B 276-278 (2000) 803 and in Czech. J. Phys. 54 (2004) D295, provides a clear physical explanation for the 1.7 meV excitation (magnetic exciton) as associated to the removal of the Kramers-doublet ground state degeneracy in the antiferromagnetic state. The crystal-field theory completed by strong intra-atomic correlations and intersite spin-dependent interactions to the Quantum Atomistic Solid State Theory (QUASST), offers the meV energy scale needed for description of magnetic and electronic properties of compounds containing open-shell 3d, 4f, 5f atoms. The derived set of CEF parameters for the U3+ state reproduces both the INS excitations, temperature dependence of the heat capacity, large uranium magnetic moment as well as its direction. PACS: 71.70.E, 75.10.D Keywords: Crystalline Electric Field, Heavy fermion, magnetism, UPd2Al3, Comment: 10 pages in RevTex4, 2 figures, in version 2 only title is changed from: Are, or not, CEF levels? We answer, ARE

We describe the experimentally revealed by Sichelschmidt et al, Phys. Rev. Lett. 91 (2003) 156401, g tensor, g_perpendicular=3.561 and g_parallel=0.17, at 5 K by means of crystal field interactions of the 4f13 configuration of the Yb3+ ion of YbRh2Si2 in a slightly orthorhombically distorted tetragonal crystal field. We have shown that the temperature dependence of the quadrupolar interactions Q(T) of the Yb nucleous will help to distinguish between Gamma_7 and Gamma_6 ground state. For the Gamma_7 ground state Q(T) is expected to exhibits an anomalous dependence. Keywords: heavy fermion, crystal field, quadrupolar moment,YbRh2Si2, Comment: 2 pages LaTeX(Elsevier Science class), 1 figure

We have shown that the observed drastic violation of the Curie-Weiss law in Na2V3O7, reported in Phys. Rev. Lett. 90 (2003) 167202, is caused by conventional crystal-field interactions and the intra-atomic spin-orbit coupling of the V4+ ion. The fine discrete electronic structure of the 3d1 configuration, with a substantial orbital moment, is the reason for anomalous low-temperature properties of Na2V3O7. According to the Quantum Atomistic Solid-State Theory (QUASST) Na2V3O7 is expected to exhibit pronounced heavy-fermion phenomena at low temperatures. This study confirm our earlier claim that the orbital moment has to be unquenched in description of 3d-atom compounds. PACS: 71.70.E, 75.10.D Keywords: crystal-field interactions, spin-orbit coupling, orbital moment, Na2V3O7, Comment: 10 pages in ReVTeX4, 3 figures

We argue that the 3A2 state considered by Oles in Phys. Stat. Sol. (b) 236 (2003) 281 for the d2 system occurring in the V3+ ion in V2O3 and LaVO3 as well as in Ti2+ ion in TiO and in many other oxides is wrong. The proper ground state is 3T1g - its 9-fold degeneracy is further split in a crystal by intra-atomic spin-orbit interactions and lattice distortions., Comment: 2 pages in RevTeX 4, submitted to Phys. Stat. Sol. B 2004-06-28, registered under No 04062802

Our success in description of recent electron-spin-resonance results on Mott insulator LaCoO3, Phys. Rev. B 67 (2003) 172401, lies in taking into account strong electron correlations among d electrons and the relativistic spin-orbit coupling. In the developed by us Quantum Atomistic Solid State Theory (QUASST) we assume that the atomic-like integrity of the 3d^6 system is preserved in the Co^3+ ion in LaCoO3 and that intra-atomic correlations are much stronger than crystal field interactions. We conclude that in LaCoO3 there is no intermediate spin state as came out from band-structure calculations. The excited states originate from the high-spin 5T2g term, being 12 meV above the ground 1A1 state. We are convinced that many-electron CEF approach with strong correlations and the atomic-scale orbital magnetism is physically adequate approach to 3d oxides. Keywords: Mott insulator, crystal field, spin-orbit coupling, LaCoO3, Comment: 5 pages, 3 figures in RevTeX4

We claim the existence of the f3 (U3+) configuration in UPd2Al3. It is in agreement with inelastic-neutron-scattering (INS) excitations and is consistent with the trivalent neptunium configuration in NpPd2Al3. We have derived set of CEF parameters for the U3+ state that reproduces the INS excitations and temperature dependence of the heat capacity. On basis of the crystal-field theory, extended to Quantum Atomistic Solid State Theory we argue that the magnetic moment of the uranium moment amounts at 0 K to 1.7-1.8 muB. Keywords: Crystalline Electric Field, Heavy fermion magnetism, UPd2Al3, NpPd2Al3 PACS: 71.70.E, 75.10.D, Comment: 6 pages in RevTeX4 within 3 figures

We have developed the crystal-field approach with strong electron correlations, extended to the Quantum Atomistic Solid-State theory (QUASST), as a physically relevant theoretical model for the description of electronic and magnetic properties of 3d-atom compounds. Its applicability has been illustrated for LaCoO3, FeBr2 and Na2V3O7. According to the QUASST theory in compounds containing open 3d-/4f-/5f-shell atoms the discrete atomic-like low-energy electronic structure survives also when the 3d atom becomes the full part of a solid matter. This low-energy atomic-like electronic structure, being determined by local crystal-field interactions and the intra-atomic spin-orbit coupling, predominantly determines electronic and magnetic properties of the whole compound. We understand our theoretical research as a continuation of the Van Vleck's studies on the localized magnetism. We point out, however, the importance of the orbital magnetism and the intra-atomic spin-orbit coupling for the physically adequate description of real 3d-ion compounds and 3d magnetism. Our studies clearly indicate that it is the highest time to ''unquench'' the orbital moment in solid-state physics in description of 3d-atom containing compounds. PACS No: 75.10.D; 71.70.E Keywords: magnetism, transition-metal compounds, 3d magnetism, crystal field, spin-orbit coupling, orbital magnetism, Comment: 52 pages, 15 figures, in LaTeX

We have calculated the discrete low-energy electronic structure in LaMnO3 originating from the atomic-like states of the strongly correlated 3d4 electronic system occurring in the Mn3+ ion. We take into account very strong intra-atomic correlations, crystal field interactions and the intra-atomic spin-orbit coupling. We calculated magnetic and paramagnetic state of LaMnO3 within the consistent description given by Quantum Atomistic Solid State Theory (QUASST). Our studies indicate that the intra-atomic spin-orbit coupling and the orbital magnetism are indispensable for the physically adequate description of electronic and magnetic properties of LaMnO3. Keywords: 3d oxides, crystal field, spin-orbit coupling, LaMnO3 PACS: 71.70Ej, 75.10Dg, Comment: 5 pages, 2 figures, in RevTex4

We provide the microscopic explanation for the localized f state observed in a heavy fermion metal YbRh2Si2 by Prof. F. Steglich's group, reported recently in Phys. Rev. Lett. 91 (2003) 156401, as associated with the strongly-correlated 4f13 configuration of the Yb atom. We derived to ground-state eigenfunctions that perfectly reproduce the observed ESR values of g_perp=3.561 and g_par =0.17: 1) G_7^1 =0.803|+-3/2> +0.595|-+5/2>-0.026|-+1/2>-0.008|+-7/2> (crystal field parameters: B_2^0 = +14K, B_4^0 = +60 mK, B_6^0 = -0.5 mK, B_4^4 = -2.3 K, B_6^4 = -10 mK with a small orthorhombic distortion B_2^2 = +0.22 K, or 2) G_6^1 = 0.944|+-1/2> + 0.322|-+7/2>-0.052|-+3/2> - 0.046|+-5/2> (B_2^0 = +8 K, B_4^0 = -60 mK, B_6^0 =+6 mK, B_4^4 = -1.78 K and B_6^4 = -5 mK with a B_2^2= +0.475 K). We express our feeling that the paper of Ref. 1 will be the turning point in the heavy-fermion subject., Comment: 3 pages, no figure, Comments to Phys.Rev.Lett. 91 (2003) 156401

We fully support the interpretation of Prof. F. Steglich, reported recently in Phys. Rev. Lett. 91 (2003)156401, that the observed \textit{below} Kondo temperature, Electron Spin Resonance (ESR) in a heavy fermion metal YbRh2Si2 is associated with the Yb3+ moment, more exactly with the strongly-correlated 4f13 configuration. We derived the ground-state eigenfunction Gamma_7^1= 0.803|\pm 3/2>+ 0.595|\mp 5/2> - 0.026|\mp 1/2> - 0.008|\pm 7/2> and crystal field parameters: B20= +14 K, B40= +60 mK, B60= -0.5 mK, B44= -2.23 K and B64= -10 mK with a small orthorhombic distortion B22= +0.23 K, that perfectly reproduce the observed ESR values of gperp= 3.561 and gpar= 0.17. These parameters also describe the observed overall temperature dependence of the paramagnetic susceptibility and predict anomalous temperature dependence of quadrupolar interactions., Comment: 5 pages, 12 references, without figure

We contest the interpretation by Gavilano et al. (Phys.Rev.Lett. 90 (2003) 167202) of violation of the Curie law behavior of the paramagnetic susceptibility at low temperatures by means of the quenching of the V4+-ion moment. These results can be understood as caused by well-known conventional phenomena like crystal-field interactions but with taking into account the intra-atomic spin-orbit coupling for the V4+ ion., Comment: 5 pages in RevTeX4, 1 figure

The orbital and spin moment of the Co2+ ion in CoO has been calculated within the quasi-atomic approach with taking into account the intra-atomic spin-orbit coupling and crystal field interactions. The orbital moment of 1.38 m_B amounts at 0 K, in the magnetically-ordered state, to more than 34% of the total moment 4.02 m_B and yields the L/S ratio of 1.04, close to the recent experimental value. This paper has been motivated by a recent paper in Phys. Rev. B 65 (2002) 125111, in which a presented theoretical approach was unable to calculate the orbital moment. PACS No: 71.70.E; 75.10.D Keywords: crystal field, spin-orbit coupling, orbital moment, CoO, Comment: 9 pages (4 pages + 5 pages of Appendix)in RevTeX 4, no figures, in ver. 2 only appendices B, D, F have been removed. Text without changes

We have shown that the observed large reduction of the effective moment and the drastic violation of the Curie-Weiss law in Na2V3O7 (Phys. Rev. Lett. 90 (2003) 167202) is caused by conventional crystal-field interactions and the intra-atomic spin-orbit coupling of the V4+ ion. The fine discrete electronic structure of the 3d1 configuration with the weakly-magnetic Kramers-doublet ground state, caused by the large orbital moment, is the reason for anomalous properties of Na2V3O7. Moreover, according to the Quantum Atomistic Solid-State Theory (QUASST) Na2V3O7 is expected to exhibit pronounced heavy-fermion phenomena at low temperatures. PACS: 71.70.E, 75.10.D Keywords: crystal-field interactions, spin-orbit coupling, orbital moment, Na2V3O7, Comment: 14 pages, 4 figures in RevTeX4, in ver. 2 only Appendix B, B1, D, D1 have been removed. Text and figures without changes

We point out that the orbital magnetism has to be taken into account in the description of real 3d-ion compounds. According to the developed by us the Quantum-Atomistic Solid-State (QUASST) theory in compounds containing open 3d-/4f-/5f-shell atoms there exists a discrete atomic-like low-energy electronic structure that predominantly determines electronic and magnetic properties of the whole compound. The relatively weak intra-atomic spin-orbit coupling is fundamentally important as it governs the low-energy discrete electronic structure., Comment: 9 pages in RevTex4, 3 figs

We have shown that the observed large reduction of the effective moment in Na2V3O7 may be caused by conventional crystal-field interactions and the intra-atomic spin-orbit coupling of the V4+ ion. The fine discrete electronic structure of the 3d1 configuration with the weakly-magnetic Kramers-doublet ground state, caused by the large orbital moment, is the reason for anomalous properties of Na2V3O7. Moreover, according to the Quantum Atomistic Solid-State Theory (QUASST), Na2V3O7 is expected to exhibit pronounced heavy-fermion phenomena at low temperatures. PACS No: 71.70.E; 75.10.D Keywords: crystal-field interactions, spin-orbit coupling, orbital moment. Na2V3O7, Comment: 4 pages in RevTex4, 4 figs

The total, orbital and spin moment of the Co2+ ion in CoO has been calculated within the quasi-atomic approach with taking into account strong correlations, crystal-field interactions and the intra-atomic spin-orbit coupling. The orbital moment of 1.39 \mu B amounts at 0 K, in the magnetically-ordered state, to more than 34% of the total moment (4.01 \mu B). The same calculations yield for NiO the orbital and total moment of 0.46 \mu B and 2.45 \mu B, respectively. PACS No: 71.70.E; 75.10.D Keywords: 3d magnetism, crystal field, spin-orbit coupling, orbital moment, CoO, NiO, Comment: 6 pages in tex+3 figs, submitted for PNSXM-03, Venice

It is pointed out that the answer on the question about the role played by spin and charge excitations will help to solve the physical origin of the heavy- fermion phenomena. Our answer is that neutral spin-like excitations are responsible for the heavy-fermion phenomena whereas the role of the charge excitations is negligible. Keywords: heavy fermion, spin excitations, charge excitations PACS No: 75.20.H, Comment: 7 pages in RevTex, no figures

We have attributed magnetism and electronic structure of V2O3 to the V3+ ions. We claim that the V3+ ion in V2O3 should be considered as described by the quantum numbers S=1 and L=3. Such quantum numbers result from two Hund's rules. The resulting electronic structure is much more complex than considered up to now, but it describes, e.g. the insulating ground state and the lowered magnetic moment, of 1.2 \muB. It turns out that the intra-atomic spin-orbit coupling is indispensable for the physically adequate description of electronic and magnetic properties of V2O3. Keywords: highly-correlated electron system, crystal field, V3+ ion, spin-orbit coupling, Mott insulators PACS: 71.70.E, 75.10.D, 75.30.Gw, Comment: 7 pages in RevTex, 1 fig

We provide the proof for the 5D term origin of an excited triplet observed in the recent electron-spin-resonance (ESR) experiments by Noguchi et al. (Phys. Rev. B 66, 094404 (2002)). We have succeeded to fully describe experimental ESR results both for the zero-field g-factor, of 3.35, and the splitting D of 4.90 cm-1, as well as for the magnetic field applied along different crystallographic directions within the localized electron atomic-like approach as originating from excitations within the lowest triplet of the 5T2g octahedral subterm of the 5D term. In our atomic-like approach the d electrons of the Co3+ ion in LaCoO3 form the highly-correlated atomic-like 3d6 system with the singlet 1A1 ground state (an octahedral subterm of the 1I term) and the excited octahedral subterm 5T2g of the 5D term. We take the ESR experiment as confirmation of the existence of the discrete electronic structure for 3d electron states in LaCoO3 in the meV scale. PACS No: 76.30.Fc; 75.10.Dg : 73.30.-m Keywords: electronic structure, crystal field, spin-orbit coupling, LaCoO3 Submitted 24.12.2002 to Phys. Rev. B., Comment: 8 pages in RevTex, 7 figs, submitted 24.12.2002 to Phys.Rev. B

The orbital and spin moment of the Co2+ ion in CoO has been calculated within the quasi-atomic approach with taking into account the intra-atomic spin-orbit coupling. The orbital moment of 1.38 \mu_{B} amounts at 0 K, in the magnetically-ordered state, to more than 34% of the total moment (4.02 \mu_{B}) and yields the L/S ratio of 1.04, close to the experimental value. PACS No: 71.70.E; 75.10.D Keywords: 3d magnetism, crystal field, spin-orbit coupling, orbital moment, CoO, Comment: 5 pages in RevTex, 3 figures, Phys.Rev. B 14.05.2002

The fundamental controversy about the electronic structure for 3d-electron states in FeBr2 is discussed. We advocate for the localized electron atomic-like many-electron crystal-field approach that yields the discrete energy spectrum, in the scale of 1 meV, associated with the atomic-like states of the Fe2+ ions in contrary to the (semi-)continuous energy spectrum yielded by band theories. In our approach the six d electrons of the Fe2+ ion form the highly-correlated atomic-like electron system 3d6 described by two Hund's rules quantum numbers S=2 and L=2 with taking into account the spin-orbit coupling. The superiority of our model relies in the fact that it explains consistently properties of FeBr2, the insulating and the magnetic ground state as well as thermodynamics and Raman low-energy spectra, using well-established physical concepts. Keywords: 3d magnetism, Hund's rules, spin-orbit coupling, crystal field, FeBr2 PACS: No: 75.50.Ee : 71.15.Mb, Comment: 8 pages in RevTex, 2 figures, Phys.Rev.B 18.06.02

Three fundamentally different electronic structures for 3d electron states in LaMnO3, discussed in the current literature, have been presented. We are in favour of the localized electron atomic-like crystal-field approach that yields the discrete energy spectrum, in the scale of 1 meV, associated with the atomic-like states of the Mn3+ ions in contrary to the continuous energy spectrum yielded by band theories. In our atomic-like approach the d electrons form the highly-correlated electron system 3d4 described by two Hund's rules quantum numbers S=2 and L=2. We take into account the spin-orbit coupling, Jahn-Teller distortion and formation of the magnetic state. The resulting electronic structure is completely different from that presented in the current literature. The superiority of our model relies in the fact that it explains consistently properties of LaMnO3, the insulating and magnetic ground state and thermodynamics, using well-established physical concepts. Keywords: 3d magnetism, Hund's rules, spin-orbit coupling, crystal field, LaMnO3 PACS: No: 71.70.Ej : 75.10.Dg : 73.30.-m, Comment: 10 pages in RevTex, 6 figures

It has been shown that for the highly-correlated d4 electronic system the spin-orbit interactions produce, even in case of the cubic crystal-field interactions, a singlet ground state. Its magnetic moment grows rapidly with the applied magnetic field approaching 4 uB for the Eg state, but only 3 uB for the T2g state. The applicability of the present results to the Mn3+ ion in LaMnO3 is discussed. Keywords: crystal-field, spin-orbit, orbital moment. PACS: 71.70.E, 75.10.D, Comment: 7 pages in RevTex, 3 figures

By this Comment we would like to point out that the authors of Ref. 1 have ignored the orbital magnetism that makes the theory irrelevant to the real systems like NiO.It causes that the calculated result for the magnetic moment of NiO substantially disagrees with the experimental observation. PACS: 71.70.E, 75.10.D, Comment: 2 pages in RevTex, no figure

We criticize the model proposed by Mila et al. (Phys.Rev.Lett. 85 (2000) 1714) for the description of the V3+ ion in V2O3 by pointing out that it is completely artificial because the condition about the degenerate (doublet) orbital ground state required for the authors' model cannot be realized in the reality. We claim that the V3+ ion should be considered as described by the quantum numbers S=1 and L=3 and with taking into account the orbital moment and the intra-atomic spin-orbit coupling. PACS: 71.70.E, 75.10.D, Comment: 3 pages in RevTex, no figures

Three fundamentally different electronic structures for 3d electron states in LaCoO3, discussed in the current literature, have been presented. We are in favour of the localized electron atomic- like approach that yields the discrete energy spectrum associated with the atomic-like states of the Co3+ ions in contrary to the continouos energy spectrum yielded by band theories. In our atomic-like approach the d electrons form the highly-correlated system 3dn described by S=2 and L=2. PACS No: 71.70.Ej : 75.10.Dg : 73.30.-m; Keywords: Mott insulators, electronic structure, crystal field, LaCoO3 Phys.Rev.Lett. 03-08-2000, Comment: 6 pages in RevTex, 3 figures in EPS

In the commented Letter Vogt et al. (Phys.Rev.Lett. 84 (2000) 2969) claim the existence of a spin-state transition in YBaCo2O5. We think that this claim about the change from the low spin to high spin state upon cooling in YBaCo2O5 is errorneous. Keywords: magnetism, 3d ions, low spin., Comment: 3 pages in RevTex, no figure