Electronic States Of Cu Research Articles

Modulating Electronic States of Cu in Metal-Organic Frameworks for Emerging Controllable CH4/C2H4 Selectivity in CO2 Electroreduction.

The intensive study of electrochemical CO2 reduction reaction (CO2RR) has resulted in numerous highly selective catalysts, however, most of these still exhibit uncontrollable selectivity. Here, it is reported for the first time the controllable CH4/C2H4 selectivity by modulating the electronic states of Cu incorporated in metal-organic frameworks with different functional ligands, achieving a Faradaic efficiency of 58% for CH4 on Cu-incorporated UiO-66-H (Ce) composite catalysts,Cu/UiO-66-H (Ce) and that of 44% for C2H4 on Cu/UiO-66-F (Ce). In situ measurements of Raman and X-ray absorption spectra revealed that the electron-withdrawing ability of the ligand side group controls the product selectivity on MOFs through the modulation of the electronic states of Cu. This work opens new prospects for the development of MOFs as a platform for the tailored tuning of selectivity in CO2RR.

Dopant-Induced Electronic States Regulation Boosting Electroreduction of Dilute Nitrate to Ammonium.

Electrochemically converting NO3 - into NH3 offers a promising route for water treatment. Nevertheless, electroreduction of dilute NO3 - is still suffering from low activity and/or selectivity. Herein, B as a modifier was introduced to tune electronic states of Cu and further regulate the performance of electrochemical NO3 - reduction reaction (NO3 RR) with dilute NO3 - concentration (≤100 ppm NO3 - -N). Notably, a linear relationship was established by plotting NH3 yield vs. the oxidation state of Cu, indicating that the increase of Cu+ content leads to an enhanced NO3 - -to-NH3 conversion activity. Under a low NO3 - -N concentration of 100 ppm, the optimal Cu(B) catalyst displays a 100 % NO3 - -to-NH3 conversion at -0.55 to -0.6 V vs. RHE, and a record-high NH3 yield of 309 mmol h-1 gcat -1 , which is more than 25 times compared with the pristine Cu nanoparticles (12 mmol h-1 gcat -1 ). This research provides an effective method for conversion of dilute NO3 - to NH3 , which has certain guiding significance for the efficient and green conversion of wastewater in the future.

Dopant‐Induced Electronic States Regulation Boosting Electroreduction of Dilute Nitrate to Ammonium

AbstractElectrochemically converting NO3− into NH3 offers a promising route for water treatment. Nevertheless, electroreduction of dilute NO3− is still suffering from low activity and/or selectivity. Herein, B as a modifier was introduced to tune electronic states of Cu and further regulate the performance of electrochemical NO3− reduction reaction (NO3RR) with dilute NO3− concentration (≤100 ppm NO3−−N). Notably, a linear relationship was established by plotting NH3 yield vs. the oxidation state of Cu, indicating that the increase of Cu+ content leads to an enhanced NO3−‐to‐NH3 conversion activity. Under a low NO3−−N concentration of 100 ppm, the optimal Cu(B) catalyst displays a 100 % NO3−‐to‐NH3 conversion at −0.55 to −0.6 V vs. RHE, and a record‐high NH3 yield of 309 mmol h−1 gcat−1, which is more than 25 times compared with the pristine Cu nanoparticles (12 mmol h−1 gcat−1). This research provides an effective method for conversion of dilute NO3− to NH3, which has certain guiding significance for the efficient and green conversion of wastewater in the future.

Highly conducting flake-like CuS nanostructured counter electrode for photoelectrochemical solar energy conversion

Fabrication of platinum (Pt) free, low cost, environmentally friendly counter electrode is highly attractive for electrochemical solar energy conversion. In this report, highly conducting flake-like CuS nanostructured counter electrode has been prepared for photosensing study and semiconductor sensitized solar cell application. Flake-like CuS nanostructures were synthesized by sulfuration of CuO nanorods grown by hydrothermal process. Scanning electron microscopy and atomic force microscopy study confirmed the growth of flake-like CuS nanostructures on glass substrates. CuS nanoflakes were highly crystalline with hexagonal phase. The various electronic states of Cu and S in CuS nanoflakes were studied using X-ray photoelectron spectroscopy. Chemically grown CuS films were highly conducting and highest conducting film was obtained at 85°C growth temperature with sheet resistance ∼20.02±0.02Ω/sq. Photoelectrochemical solar cell (PEC) was fabricated using CdS decorated TiO2 nanorods as working electrode and CuS film as counter electrode. The short circuit current density, open circuit voltage and power conversion efficiency of the PEC device were found to be ∼4.8 A/m2, ∼0.38 V and ∼0.17%, respectively.

Effective CO2 electroreduction toward C2H4 boosted by Ce-doped Cu nanoparticles

• An effective strategy has been established by doping Ce into Cu NPs to tune the electronic state of Cu. • It attains the faradaic efficiency of C 2 H 4 as high as 53% with a current density of 150 mA/cm 2 . • Such performance is about 2.8-fold increase when compared with Cu NPs. • The electronic structure regulation and defective sites facilitate highly efficient C 2 H 4 production from CO 2 electroreduction. Coupling another metal element tends to produce catalytic controls of high activity and selectivity. However, this action is still poorly explored to improve the selectivity of the electroreduction of CO 2 to C 2 H 4 with high energy density. Herein, Ce-doped Cu nanoparticles (Ce-Cu NPs) are synthesized by one-step co-reduction method and presented a preferable example that promotes selective transformation of CO 2 to C 2 H 4 in a flow-cell configuration. Thereinto, high faradaic efficiency (FE) of C 2 H 4 for Ce-Cu-2 NPs could reach 53% with the current density of 150 mA cm −2 , which is 2.8 times higher than that of Cu NPs. The outstanding performance mainly stems from tailoring the doped-Ce content shrinks particle sizes and forms oxygen defects due to the electron effect of nearby Ce atoms, boosting local electronic re-distribution of Cu. Meanwhile, in-situ Raman spectroscopies evidenced that the doping of Ce can enhance Cu site to bond *CO, which were beneficial to C–C coupling and thus endowed the catalyst with the superior catalytic performance in CO 2 electroreduction toward C 2 H 4 .

Highly Selective Electrocatalytic Reduction of CO2 into Methane on Cu-Bi Nanoalloys.

Methane (CH4), the main component of natural gas, is one of the most valuable products facilitating energy storage via electricity conversion. However, the poor selectivity and high overpotential for CH4 formation with metallic Cu catalysts prevent realistic applications. Introducing a second element to tune the electronic state of Cu has been widely used as an effective method to improve catalytic performance, but achieving high selectivity and activity toward CH4 remains challenging. Here, we successfully synthesized Cu-Bi NPs, which exhibit a CH4 Faradaic efficiency (FE) as high as 70.6% at -1.2 V versus reversible hydrogen electrode (RHE). The FE of Cu-Bi NPs has increased by approximately 25-fold compared with that of Cu NPs. DFT calculations showed that alloying Cu with Bi significantly decreases the formation energy of *COH formation, the rate-determining step, which explains the improved performance. Further analysis showed that Cu that has been partially oxidized because of electron withdrawal by Bi is the most possible active site.

Magnetic and electric properties, ESR, XPS and NEXAFS spectroscopy of CaCu3Ti4O12 ceramics

ESR, XPS and NEXAFS spectra, as well as magnetic and electric properties of CaCu3Ti4O12 synthesized by the solid-phase method within 6,12,24,48 and 60 h were studied. The analysis of magnetic susceptibility of CaCu3Ti4O12 and magnesium-containing solid solutions of CaCu3-3xMg3xTi4O12 revealed antiferromagnetic exchange interactions between Cu paramagnetic atoms, while the effective magnetic moment of copper atoms corresponds to the electronic state of Cu(II). In CaCu3Ti4-4хMg4хO12-δ samples within the whole concentration range the impurity phase MgTiO3 was observed. The magnetic properties of calcium copper titanate were found to be inconsistent depending on the synthesis duration. The extreme point of magnetic susceptibility was found among samples synthesized within 48 h. Modelling and interpretation of the XPS spectra of CaCu3Ti4O12 were performed. Based on the NEXAFS and XPS spectroscopy data, copper and calcium atoms in ceramics display oxidation state +2, while titanium atoms – Ti(IV). ESR spectra of CaCu3Ti4O12 samples show an exchange-narrowing signal from copper (II) atoms at g = 2.15. In the ESR spectra of CaCu3-3xMg3xTi4O12 the only intense exchange-narrowed line of Lorentzian form of Cu2+ ions is observed. The impedance spectroscopy study of electric properties of CaCu3Ti4O12 found the media to feature temperature-dependent reach-through conductivity with activation energy of 0.79–0.71 eV. At 255–300°С, the dominant polarization process is in line with the Gerischer model. It indicates the formation of anionic-cationic associates accompanied by decreased low-frequency capacitance of the samples. With temperatures of over 300°С the samples start displaying ion-migrating polarization which contributes to higher capacitance and dielectric loss at low frequencies. As the temperature grows further to 400°С, the ion migration process gets to dominate within the whole frequency range under study. Based on the study, a conclusion was made on movable cations of copper participating in the polarization process at room temperature.

Effect of the Electronic State of Cu, Ag, and Au on Diesel Soot Abatement: Performance of Cu/ZnO, Ag/ZnO, and Au/ZnO Catalysts.

Noble metals such as Au, Ag, and Cu supported over semiconducting ZnO are well-known heterogeneous oxidation catalysts. All of them have been utilized for the oxidation of diesel soot with varied success. However, Au-supported ZnO is seen to be superior among them. Here, we present a comparative study of all these three catalysts for diesel soot oxidation to explain why Au/ZnO is the best among them, demonstrating the contribution of electronic states of metals in composite catalysts. The electronic states of Cu, Ag, and Au determined by X-ray photoelectron spectroscopy on 1 wt % Cu/ZnO, 1 wt % Ag/ZnO, and 1 wt % Au/ZnO catalysts were correlated with their diesel soot oxidation activities. Although all three catalysts present reasonable diesel soot oxidation activities at relatively low temperature, 1% Cu/ZnO and 1% Ag/ZnO oxidize only about 60% of the deposited diesel soot around 250 °C and 1% Au/ZnO oxidizes 100% of the deposited diesel soot, at a temperature as low as 230 °C. The activity of the catalysts is attributed to the formation of stable M0–Mδ+ bifunctional catalytic sites at the metal–ZnO interface, which enhances the contact efficiency of solid diesel soot on Mδ+ and generates the superoxide species on M0 moieties. The stability of the bifunctional M0–Mδ+ sites is controlled by the electronic interactions between the metal (M) and n-type semiconductor ZnO at their interface. Very high activity of 1% Au/ZnO is attributed to the presence of Au3+ at the catalyst surface, which generates a stronger Coulombic force with diesel soot electrons. We demonstrate a direct relation between the diesel soot oxidation activity of these three metals and their electronic states at the catalyst surface.

Cu and CuPb Electrodes Electrodeposited from Metal Oxides in Hydrophobic Protic Amide-Type Ionic Liquid/Water Mixture for Nonenzymatic Glucose Oxidation

Cu and CuPb were electrodeposited from the mixture of water and a protic amide-type ionic liquid (IL), the protonated betaine bis((trifluoromethyl)sulfonyl)amide ([Hbet][TFSA]), in which CuO and PbO were dissolved. The electrodeposited Cu electrode showed electrocatalytic activity toward glucose oxidation in alkaline conditions, and the activity was significantly enhanced once Pb was doped. Activity enhancement might result from the changes of the surface morphologies and the electronic states of Cu, which were concluded according to the SEM observations and XPS analyses.

Rovibrational Characterization of High-Lying Electronic States of Cu2 by Double-Resonant Nonlinear Spectroscopy.

The available knowledge of the electronically excited states of the copper dimer is limited. This is common for transition metals, as the high density of states hinders both experimental assignment and computation. In this work, two-color resonant four-wave mixing spectroscopy was applied to neutral Cu2 in the gas phase. The method yielded accurate positions of individual rovibrational lines in the I-X and J-X electronic systems. This revealed the term symbols for the I and J states as 1Πu (1u) and 1Σu+ (0u+), respectively. For the 63Cu2 isotopologue, accurate molecular constants were obtained. The characterization of the J state finally allowed decisive determination of its electron configuration. The J state is obtained from the ground state by promotion of a 3dπg electron into the weakly bonding 4pπu molecular orbital. From the data analysis, lifetimes of the I state (between 10 ps and 5 ns) and J state (66 ns) were inferred.

Low Cost Cu/ZnO as Low Temperature (150 °C) Catalyst for Diesel Particulate Matter Oxidation

The catalytic behavior of hydrogen-reduced copper loaded ZnO, SiO2, and TiO2 has been investigated for diesel particulate matter(PM) oxidation. 5 %Cu/ZnO showed a strong diesel PM oxidation activity at 150 °C. XPS spectroscopy was utilized to study the electronic states of Cu in Cu/ZnO catalyst. Presence of Cu1+ ions at the surface of the catalyst even after its use in PM oxidation cycles was assigned responsible for its high catalytic performance. The high stability of Cu1+ is explained on basis of the isoelectronic interactions of Cu1+ (3d10) with Zn2+ (3d10) at the Cu2O–ZnO interface. Cu/SiO2 and Cu/TiO2 were not active for this reaction probably due to the absence of Cu1+ which could not be stabilized by Ti4+ or Si4+. Results indicate that 5 %Cu/ZnO catalyst can be utilized for the abatement of diesel engine emissions even from the starting point of cold engines.

Magnetic Determination of the Electronic State of Cu and Exchange Interactions in the $\alpha $ - and $\beta $ -Phases of Molecular Semiconductor Copper Phthalocyanine (C32H16N8Cu)

Using the analysis of the magnetization data in the $\alpha $ - and $\beta $ -phases of copper phthalocyanine (CuPc) samples, the electronic state of Cu and exchange interactions are reported. After verifying the crystal structure of the powder samples using X-ray diffraction, the temperature dependence (2–250 K) of the magnetization $M$ of both samples was measured in magnetic field $H=1$ kOe and isothermally at 2 and 5 K in $H$ up to 90 kOe. The data were analyzed first using the modified Curie-Weiss law, $\chi = \chi _{o}+ C/(T+\theta )$ , showing good fit for $T >4$ K and yielding $\theta =2.3$ K (0.2 K) for $\alpha $ -CuPc ( $\beta $ -CuPc) and spin $S=1/2$ characteristic of Cu2+. The data were next fitted to the Bonner-Fisher model for $S=1/2$ antiferromagnetic Heisenberg chain showing an excellent fit to all the $M$ versus $T$ data and yielding the Cu2+–Cu2+ exchange constant $J/k_{B}=3.4$ K (0.4 K) for the $\alpha $ -CuPc ( $\beta $ -CuPc). The isothermal data of $M$ versus $H$ are analyzed taking exchange coupling into account. The large difference in the magnitudes of $J/k_{B}$ for the two phases is discussed in terms of the differences in their crystal structures.

Ab Initio Study on Pressure-Induced Phase Transition in LaCu3Fe4O12

The electronic structure and magnetic ordering in LaCu3Fe4O12 are theoretically studied by means of ab initio calculations. To clarify the microscopic mechanism for the experimentally observed phase transitions induced both by pressure and temperature, the cell-volume dependence of total energy is calculated. It is found that the electronic structure changes from insulating to metallic as the Cu valence shifts from nonmagnetic Cu3+ (S = 0) to spin-polarized Cu2+ (S = 1/2) at the transition pressure (or temperature). The electronic state of Cu is important since it is coupled with the metallicity of the electronic structure via the inter-site charge transfer. The pressure-induced phase transition in LaCu3Fe4O12 is explained by the difference in the bulk modulus between the insulating ground state and the metallic high-pressure phase. The mechanism for the temperature-induced phase transition is also proposed in terms of the magnetic configurational entropy of the magnetic moment of Cu spins.

Local versus global electronic properties of chalcopyrite alloys: X-ray absorption spectroscopy and ab initio calculations

Element-specific unoccupied electronic states of Cu(In, Ga)S2 were studied as a function of the In/Ga ratio by combining X-ray absorption spectroscopy with density functional theory calculations. The S absorption edge shifts with changing In/Ga ratio as expected from the variation of the band gap. In contrast, the cation edge positions are largely independent of composition despite the changing band gap. This unexpected behavior is well reproduced by our calculations and originates from the dependence of the electronic states on the local atomic environment. The changing band gap arises from a changing spatial average of these localized states with changing alloy composition.

Grafting of Precoordinated Cu2+–N-(2-Aminoethyl)aminopropylsilane Complexes onto Mesoporous Silicas and the Adsorption of Aqueous Selenate on Them

N-(2-Aminoethyl)aminopropylsilane (AeAptes) was coordinated with Cu(2+) with Cu:AeAptes ratios of 1:1 and 1:2. These were then grafted onto MCM-41 [the products being denoted as Cu(en)-MCM-41 and Cu(en)2-MCM-41, respectively] and SBA-15 [the products being denoted as Cu(en)-SBA-15 and Cu(en)2-SBA-15, respectively]. The periodic structures of these mesoporous silica frameworks were well-retained after grafting. UV-visible and EPR spectroscopies were used to analyze the coordination structure of Cu(2+), revealing the structure expected from the ratio of Cu(2+) to silane. We also prepared Cu(en)- and Cu(en)2-M7D by the same procedure using Cab-O-sil M7D silica. In contrast to the complexes grafted onto the mesoporous silicas, no significant differences were found in the d-d transition band positions, the g-tensor, and hyperfine coupling constants between Cu(en)-M7D and Cu(en)2-M7D. The structural parameters of these were almost the same as those of Cu(en)-MCM-41 and Cu(en)-SBA-15, suggesting that the grafting onto M7D resulted in the transformation of coordination structure of Cu(2+)(AeAptes)2. The adsorption of selenate was analyzed using the Langmuir equation. The adsorption capacities for Cu(en)- and Cu(en)2-mesoporous silicas were Se/Cu = 0.5 and 1.0, respectively, while the Langmuir coefficients for Cu(en)2-mesoporous silicas were more than twice those for Cu(en)-mesoporous silicas. However, no significant differences in these two parameters were found between Cu(en)- and Cu(en)2-M7D; Se/Cu = 0.53-0.56 at saturation and the Langmuir coefficients were the same. The decomposition of the coordinated Cu complex after grafting onto M7D is discussed with respect to the structure of the silica surface. The electronic state of Cu in Cu(en)- and Cu(en)2-mesoporous silicas was analyzed by XANES spectroscopy before and after the adsorption of selenate.

Electronic states of Cu(110) investigated with angle-resolved two-photon photoemission spectroscopy

Occupied and unoccupied electronic states of Cu(110) were investigated with angle-resolved two-photon photoemission spectroscopy with an energy resolution of 30 meV. The high energy resolution enables the individual $n$ $=$ 1 and 2 image-potential-derived structures to be distinguished. The $n$ $=$ 1 structure was 0.85 eV below ${E}_{\mathrm{vac}}$ at $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}$. The effective mass of the electron for the structure was the same for both dispersions along the $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}\mathrm{X\ifmmode \bar{}\else \={}\fi{}}$ and $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}\mathrm{Y\ifmmode \bar{}\else \={}\fi{}}$directions within the experimental error. The $n$ $=$ 2 structure appeared in the ${L}_{{2}^{\ensuremath{'}}}$-${L}_{1}$ gap along the $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}\mathrm{Y\ifmmode \bar{}\else \={}\fi{}}$ direction, and it did not appear at $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}$, or along the $\mathrm{\ensuremath{\Gamma}\ifmmode \bar{}\else \={}\fi{}}\mathrm{X\ifmmode \bar{}\else \={}\fi{}}$ direction, which means that the $n$ $=$ 2 structure was strongly affected by the bulk band. In this paper, other two-photon photoemission structures and dispersions are compared with results reported in the previous literature.

Measured density of copper atoms in the ground and metastable states in argon magnetron discharge correlated with the deposition rate

In a dc-magnetron discharge with argon feed gas, densities of copper atoms in the ground state Cu(2S1/2) and metastable state Cu*(2D5/2) were measured by the resonance absorption technique, using a commercial hollow cathode lamp as light source. The operating conditions were 0.3–14 µbar argon pressure and 10–200 W magnetron discharge power. The deposition rate of copper in a substrate positioned at 18 cm from the target was also measured with a quartz microbalance. The gas temperature, in the range 300–380 K, was deduced from the emission spectral profile of N2(C 3Πu − B 3Πg) 0–0 band at 337 nm when trace of nitrogen was added to the argon feed gas. The isotope-shifts and hyperfine structures of electronic states of Cu have been taken into account to deduce the emission and absorption line profiles, and hence for the determination of atoms' densities from the measured absorption rates. To prevent error in the evaluation of Cu density, attributed to the line profile distortion by auto-absorption inside the lamp, the lamp current was limited to 5 mA. Density of Cu(2S1/2) atoms and deposition rate both increased with the enhanced magnetron discharge power. But at fixed power, the copper density augmented with argon pressure whereas the deposition rate followed the opposite trend. Whatever the gas pressure, the density of Cu*(2D5/2) metastable atoms remained below the detection limit of 1 × 1010 cm−3 for magnetron discharge powers below 50 W and hence increased much more rapidly than the density of Cu(2S1/2) atoms, over passing this later at some discharge power, whose value decreases with increasing argon pressure. This behaviour is believed to result from the enhancement of plasma density with increasing discharge power and argon pressure, which would increase the excitation rate of copper into metastable states. At fixed pressure, the deposition rate followed the same trend as the total density of copper atoms in the ground and metastable states. Two important conclusions of this work are (i) copper atoms sputtered from the target under ion bombardment are almost all in the ground state Cu(2S1/2) and hence in the plasma volume they can be excited into the metastable states; (ii) all atoms in the long-lived ground and metastable states contribute to the deposition of copper layer on the substrate.

Strong molecular field effect from Gd on 3d-electronic states of Cu in concentrated Gd-Cu non-crystalline alloys

The molecular field effect from Gd on the 3d electronic states of Cu was studied from both a macro-scopic magnetization measurement and a micro-scopic way of magnetic Compton profile MCP in the rich content of Gd where the molecular field from Gd was increased as high as possible. From magnetization measurement, the magnetic moment of Gd was estimated to be about 7.0μB in Gd67Cu33 and Gd70Cu30 alloys, respectively. The Curie temperature Tc was found to increase gradually from 140 K for Gd60Cu40 to 150 K for Gd70Cu30. The MCP measurement revealed that some kinds of spin-polarization of 3d electrons in Cu were not detected effectively. That is, the 3d electronic states of Cu were stable and not affected effectively even in the stronger molecular field applied.

First principles study of electronic structure of CeNi 4Cu

The results of the electronic structure investigation of CeNi 4Cu with the hexagonal CaCu 5-type structure have been presented. The results show domination of the 3d electronic states of Ni below the Fermi energy as well as the participation of 3d electronic states of Cu in the density of states in the energy region from −5 eV to −1 eV. The itinerant electrons of Ni and Cu are found to play a significant role in increase of the degree of hybridisation of Ce 4f with Ni 3d bands at the Fermi level. The hybridisation effects in valence band of CeNi 4Cu are discussed. The calculated value of electronic specific-heat coefficient does not suggest a heavy-fermion behaviour in the studied system.

Towards accurate all-electron quantum Monte Carlo calculations of transition-metal systems: Spectroscopy of the copper atom

In this work we present all-electron fixed-node diffusion Monte Carlo (FN-DMC) calculations of the low-lying electronic states of the copper atom and its cation. The states considered are those which are the most relevant for the organometallic chemistry of copper-containing systems, namely, the (2)S, (2)D, and (2)P electronic states of Cu and the (1)S ground state of Cu(+). We systematically compare our FN-DMC results to CCSD(T) calculations using very large atomic-natural-orbital-type all-electron basis sets. The FN-DMC results presented in this work provide, to the best of our knowledge, the most accurate nonrelativistic all-electron correlation energies for the lowest-lying states of copper and its cation. To compare our results to experimental data we include the relativistic contributions for all states through numerical Dirac-Fock calculations, which for copper (Z=29) provide almost the entire relativistic effects. It is found that the fixed-node errors using Hartree-Fock nodes for the lowest transition energies of copper and the first ionization potential of the atom cancel out within statistical fluctuations. The overall accuracy achieved with quantum Monte Carlo for the nonrelativistic correlation energy (statistical fluctuations of about 1600 cm(-1) and near cancelation of fixed-node errors) is good enough to reproduce the experimental spectrum when relativistic effects are included. These results illustrate that, despite the presence of the large statistical fluctuations associated with core electrons, accurate all-electron FN-DMC calculations for transition metals are nowadays feasible using extensive but accessible computer resources.